my (F20) boyfriend (M19) says he needs to lose me to improve himself

if you could please take time out of your day to read this and give advice, i would sincerely appreciate it and be grateful.

side note; we’ve had a really fulfilling relationship aside from the things I’m going to list. he is extremely giving, loving (usually, and recently not loving) and emotionally supportive. i see him as my best friend. this is genuinely someone i see my future with. I’ve met his family, and since we were forced into a long-distance circumstance, its been going south. but overall, he has been a great boyfriend and i genuinely vouch for the kind of connection and commitment we have for each other, and have expressed toward each other. i know he wants to marry me, and i want to marry him.
we’ve had a long story and been together for almost a year now, and i’ll start at the major things he’s done that have kept our relationship rocky. in the beginning of our relationship, he was messaging his ex that she will always hold a special place in his heart and that he loves her “for closure” that they didn’t have (they broke up very soon before we got together), and i saw the texts and was really hurt. he said the words didn’t mean anything, he just wanted to leave off on a good note. we’ve had more issues with conflict as he has difficulty taking accountability and gets immediately defensive (he doesn’t trust my “intentions” and thinks i am attacking him essentially– however, when i have approached things calmly and with my feelings only included with no attacking manner, he still gets defensive and mean sometimes so honestly, i don’t know.) he also, while were committed, sent a flirty text to one of his girl friends. he apologized a lot over this after isolating himself from me for a couple of days.

then, he was 18 (19 now), and was speaking to this 14 year old girl. i was spending a couple days w him and i was constantly asking him if he’s okay with me staying, that i can go if he needs some alone time because i don’t wanna like overcrowd him or anything. he said no it’s okay, he doesn’t need me to go and that he’s enjoying me being around. i said this a couple more times to make sure. meanwhile, he’s texting this 14 year old girl that I’m a “codependent motherfucker” and a lot more immature shit. i was extremely hurt seeing these texts. i eventually forgave him, and we went onto becoming long distance due to a lot of external things like his family not being able to afford his college out of state if he fails classes. until months and months later where i found he was still talking to her! and after another argument where he defended it, he finally stopped talking to her, and apologized.

then, a couple months down the line, i find out he lied to me. about A LOT. every single girl friend he had. i asked him MULTIPLE times in our relationship “have you ever felt romantic feelings/been liked by any of your girlfriends?” as a curious question. it would be good to know, and he had many of them. i assured him it was never to like break their contact and i had no impure intentions, as of course, it would’ve been years ago that this happened. he adamantly told me no. i never fully believed him, so i’d lightheartedly ask him a couple more times and wrap it up with me saying it’s okay if he did like them or they liked him in the past. he always said NO.

i found out this wasn’t true. i looked through his phone text messages and found EVERY SINGLE GIRL FRIEND HE HAS EVER HAD AND STILL HAS CONTACT WITH, he had flirted with, they had flirted with him, and its the same ones he lied about and continued to speak to. and there was one, who was the best of all, we’ll call her jade. all these past months, he’d been emotionally forming a strong bond with her over our relationship problems. he sent her so many arguments of ours, and she would say stuff like “tell her to die” “i don’t think you’re wrong in this situation” , etc. and they would bond over it, for since February of this year when they began talking again, and i found out in july. emotional cheating. she would be like “tell your gf I’m lesbian so you can play video games with me!” (he told her i wouldn’t be okay with them gaming together– he never asked, and i would’ve definitely NOT SAID NO! i asked if we could all play with one of his other girl friends (coincidentally the only girl friend he didn’t flirt back with.) so he just lied.) and she would constantly say that, tell her I’m gay, tell her I’m a lesbian– she’s not btw. and in every argument, he never provided context, and i would be framed as the bad guy. one of them, i was sad that me and him had no time together that day. we are long distance, and sparing an hour of his non-busy day would’ve been nice instead of him playing video games all day. he didn’t feel the same way, even though we had agreed that we would both spend time with each other everyday even if its for 30 minutes or an hour. he sent her the whole argument, and never told her that we agreed on that, and she was like “you can’t have one day to yourself?” except, no, it’s not that he can’t have one day to himself, its that WE AGREED wed do this everyday to keep our relationship strong despite the distance. they’d also reminisce about their old memories together, he’d tell her to break up w her bf bc he’s “toxic”, and the worst part… he would triple quadruple message her. he’d send her mini paragraphs explaining how he’s always there for her, and that he misses talking to her, he’s grateful for her being around and that he cares about her a lot. VERY DETAILED, and a lot of double texting if she didn’t respond. A LOT. and the texts, seeing that effort he put in to send her such detailed intricate messages, hurt me so badly.

so i felt that he emotionally cheated on me, as it is defined as an emotional affair where two people bond over their fragmented relationships and rant about their relationships and develop a closer tight-knit bond from it (ours was not even fragmented, he just .. has a lot to work on in terms of conflict.. (gaslighting, defensiveness, not taking accountability, avoidant attachment, emotionally withdrawing) and that’s not to say at the time i didn’t either — i had a short fuse, got angry fast and said things i didn’t mean. i have now improved heavily on this and am expressive on my feelings and always try to take his perspective, but he’s gotten WORSE ever since this personal improvement of mine). i BEGGED him, to never lie again, that lying DESTROYS me and that by lying he would taking a step in completely destroying my emotions and feelings.

ever since this, we had arguments, we argued a lot because i felt angry and hurt at the time. i wondered what i did to deserve it all. i thought i had been a good girlfriend, despite my past and issues. i had gone through a DV situation where it affected me heavily, and i’ve been healing from it for a couple of years now. I’m not the best i can be, and i can be very emotional, but i am extremely communicative. i have always been expressive of my feelings and asked him to be the same way. i told him before we even dated that i was big on communication. without it, i can’t do relationships. and so, i heavily communicated, i stayed with him because i love him, and i told him how much it hurt me. i got angry at times, and i shouldn’t have. i said the wrong things that were not at all productive, but i learned from it. we stopped arguing about him cheating, but it went onto just more short arguments because of the tensity we had around each other. i don’t think he enjoys feeling “at fault”, as much as he knows it is his fault. it is something he struggles with (“feeling accused”) and he gets defensive. so, he says, that it all happened because of all the arguments. but the arguments stopped, and he began to emotionally withdraw. he started saying for the first time “i wanna be alone” which is okay, but he would be mean, cold, distant the whole day when he said this. completely void of emotion, lack of consideration for my feelings, and when i expressed this, he would say he’s not being mean even though he clearly was, and eventually after a long discussion, realized why i felt that way. i was heavily improving at this point in time– i no longer got angry, i was open about my feelings and it was something he had said he wished id do (he wanted me to say I’m sad more, and express feelings more), but ever since i started doing this, he GOT WORSE. almost like.. he couldn’t have an excuse anymore for his cruelty toward me. i was completely being beat down, he called me something really horrible because i was upset and he had NEVER called me ANYTHING like that before.

he continued to lie, a lot. about so many random things. he would just lie, and lie, and i would always catch it. it hurt me a lot because it’s the one thing i begged him not to do. he began to be meaner, colder, more emotionally distant, say he needs more alone time. and with this, the majority of what he would do is play video games. and even now, i haven’t fully lost hope of him coming back to who he used to be because i love him so much.

we broke up a couple of days ago because he said he needs to lose me to know what he had. “You don’t know what you had until it’s gone” that is what he quoted. i wondered, why can’t he improve just being with me? he said he wants to come back to me, to marry me, but that he is in a slump and can’t self-improve with me as his girlfriend. it doesn’t make any sense to me. he says he doesn’t wanna hurt me anymore and he knows he will continue to hurt me and do the wrong things and he wants to spare me of it and work on himself. that he’s going to continue to say he’s “taken” to people. it’s been a couple of days now, and it hurts so much. i don’t know what to do. i am so hurt, and i don’t know what i did to deserve this. i have been exactly the kind of person i aspired to be. open, honest, kind. but it is never enough. does it make sense for him to say he cannot improve in a relationship with me?

tldr
me and my boyfriend have been through a lot and he is extremely defensive and doesn’t like to take accountability. he says due to my past explosive anger that I have now improved on, he holds resentment and cannot improve himself while being with me and knows he will continue to hurt me if we stay together, but that he wants to ultimately be with me after his self-improvement journey, and that he will say he is “taken” to others. what do i do?