tl;dr my partner hates my ex bff but i want them back in my life

this is a throwaway for obvious reasons and i plan on talking about this with my therapist but it weighs so heavy on me. i at least need a void to scream into. i’m in my first long term (key word long term, i’ve been in a lot of relationships not lasting more than 6 months) relationship. my girlfriend (23F) and I (21F) have been together two years and i love her deeply. she’s brought a calm to my life i never thought imaginable and i appreciate her very much. we have discussed marriage and that’s the path our relationship is on. and while i love her so much and want to be with her forever, i keep finding myself checked out of our relationship thinking about an old friend.

we were inseparable for a long time but we ended on strange terms to say the least. he and i used to see one another daily and i was close with his family. most people confused us as a couple and we laughed it off, saying we were just close friends. a few years go by, we both date other people and break up and eventually, in my freshmen year at college i was in a relationship with someone i’d been off and on with since high school and things just kept not working because they kept cheating. one night my friend (let’s call him A) comes over to drink with my boyfriend, his friend, and i. the old “what if we dated” conversation came up in which we both agreed it was bound to happen eventually. We made a pact to be married at 30 if we both remained single. that night my boyfriend ran off to go do drunk shit with his friend and i was left with A. Needless to say, i ended up spending the night with him. my boyfriend and i broke up and after that we slept together a few times. after the first i clarified that we were still okay. that nothing had changed. within a month he had completely abandoned me. he didn’t speak to me for six months. when he left i lost myself. i went a little insane. when he came back i just focused on punishing him and pushing him away.

Meanwhile i meet my lovely girlfriend. she absolutely hates A. she’s hated him for years since before she met me. i’m committed to her, ive built a home with her. i hate myself for the cheating i did in my past and i never want to do it again. and i won’t. but in time, A has moved on too. he has a wife and a baby on the way and i’m happy for him. we’ve spoken but i feel like any kindness i show him would make my girlfriend feel betrayed so i’m cold with him. pushing him away more when i want him back in my life so badly. i think about him at least once a day if not all day and i need to let go for my own sake and the sake of my relationship but something deep in me wants to reach out and just speak to him and it torments me. even thinking so much about him feels like cheating but more than anything i just miss my best friend. no one has ever understood me like he did. no one ever treated me so well or cared so much for me. but i know reaching out could be detrimental to my relationship. my girlfriend hates him. but i love my girlfriend so i just feel so torn and hurt. i want to see A and have a real conversation without fake bitterness but that feels wrong. any advice is good advice please help

tl;dr my partner hates my ex bff but i want them back in my life