My (21M) ex-gf (23F) cheated on me and now desperately wants me back

I (21 M) just experienced my first break-up with my ex-gf (23 F) and now she acts crazy.
She left in 2017 her boyfriend (now a college professor) for me (a high school student) and she told me multiple times how much obsessively in love she was with me. Throughout our relationship, she made me multiple gifts and invited me to the restaurant much more frequently than I invited her, as she came from a much wealthier family than mine.

In 2021, after 4 years of a happy relationship, we decided to move in together in the new student city we were going to live in. She and I are both students at this time. My gf immediately took the role of the traditional housewife, cooking me dinner and lunch and taking care of the decoration of our flat. I was a bit uncomfortable at first with the fact that she wanted to play the role of the perfect spouse but then I let her do it as I’ve to admit having meals prepared every evening was pretty nice.

In September 2021, a guy hit on her, for the sake of anonymity, let’s call him Fool. According to my gf, Fool is the opposite of me. While I workout 4-5 days a week, he does not. While I’m a rather stoic and unemotional kind of person, Fool is emotionally unstable and has psychiatric problems. While I rather look masculine, he is defining himself as genderfluid. In September, my gf declined Fool’s invitation for a drink. That’s expected because I always told my gf that I’d never forgive infidelity. If she ever cheated on me, I’d then remove her from my life.

Fast-forward to May 2022, my gf sent Fool a message, and they end up going to the library together and then had sex together multiple times for the 2 weeks before she asked me to open up our relationship. When she asked me to open our relationship, I told her that I’d leave her a week to take all her stuff out of our flat otherwise I’d put it to waste disposal. When she and I had the discussion about “opening the relationship”, she hadn’t confessed to me yet that she cheated on me for 2 bloody weeks. We broke up on first of June 2022.

She then tried to get into a relationship with fool, but left him after 2 weeks because he was way more emotionally invested into her than she was into him. A few days after the break-up I blocked her account on all social medias and set up an instagram account (to upload photos of the exotic trip I had planned with a friend in the end of June), a Tinder and a Bumble account to set up dates with new girls. In the end of June, I traveled to another continent, got a considerable number of Tinder matches and ended up having sex with a girl less than 24 hours after my arrival. Meanwhile, I was posting photos on my instagram account of my holidays. My ex-gf later confessed to me that she had created a fake account on Instagram to stalk me, and that each day she would watch my list of female followers grow (these were my tinder matches).

Then, after my trip, I went back to my hometown and that’s when she starts going crazy. She came to my place at 1 am, ringing the doorbell frenetically. She woke me up, and I opened her the door, still half-asleep. She then proceeded to tell me how she could not get over our relationship, was still in love with me, that we’d never meet someone else with who we’d share such a connection, blah blah blah…

I had sex with her 2 times and I told her that I was hesitant, but I could maybe get back with her since she had not tell me yet that she had cheated on me. So I told her I might consider getting back with her, although I needed time to make up my mind. Then she started crying, and she told me she hadn’t told me the whole truth. That’s when she confessed to me that for 2 weeks, she had sex with Fool while also having sex with me. When she told me that, I felt crushed inside and as if my heart got split in two. My trust for her was instantly gone, and I told her that a few seconds ago I was hesitant whether I’d take her back, but now I was 100 percent confident I’d never get back with her.

Then she literally begged me and went on her knees, imploring me to get back with her for an hour or two. I told her I had to think and that maybe I’d find the inner-strength to forgive her, although I’d no longer be exclusive with her, and I was planning to still see the 4 dates I had planned this week (I also showed her my tinder account and my 50+ number of matches).

Then I had sex 3 more times that day with her and took her back to her place, letting her believe that there was a chance that I’d take her back. After talking with my friends and listening to my feelings, I went to the conclusion that I could never forgive her the feeling of betrayal and that she definitively went over my limits. That’s when she started screaming and crying frenetically on the phone, telling me I’ve never loved her and that she stayed for 5 years in a relationship with someone who didn’t like her, that all she did was take care of me in difficult times, setting the stage for the next girl after her.

Upset by her words, I told her to come back to my home, which she did, and I calmly explained to her that my feeling of betrayal was just too much and that she should never have cheated on me, this was my boundary, and she did not respect it. She screamed and cried again and told me she had lost appetite and sleep, her doctor (which is her father) had given her anxiolytic, and she told me that she’d leave this world. I told her that I could not forgive her but that her loved-ones could and that she had to told her family and close-friends that she cheated on me. After she said again that she should disappear from this world, I called her mother and told her that her daughter is not going well, so my gf’s brother ended up picking her up. Just before my gf left, I asked her whether she would get back with me if I sent her a message in September telling her that I had forgiven her. She told me she would without hesitation.

The day after, I sent my ex-gf a message telling her we would never be back together, that she betrayed both my trust and my love, that I was her best option between me and Fool but that she was no longer mine. I also wrote to her that there were many girls that would never cheat on me, lie to me, and use suicide-threats against me and that unfortunately for her, she wasn’t one of those girls. My ex-gf answered : “thank you. good bye”.

30 mins later, her mom sent me a message asking me not to contact her daughter anymore. I replied to her that I had blocked her daughter on all social medias since over a month and that had she not came to my place in the middle of night, we wouldn’t have had any interactions. I also told her that the fact her daughter had protected/unprotected sex with someone while being with me was deeply disappointing and upsetting and that my gf’s father, as a doctor, could certainly relate to my concerns.

I just feel so angry because my gf’s family behaves as if somehow I’ve done something wrong while I’ve always be a trusty and loving bf and my gf cheated on me, potentially gave me stds (I get tested in 2 weeks) and broke my trust. I’m 100 % sure I don’t want to get back with her (I was already sure of that 48 hrs after we broke up in June) but I just feel too moved by these events. The feeling of betrayal is painful and I feel so disrespected.

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\*\*TL;DR\*\* After 5 years of happy relationship, my gf cheated on me. 6 weeks later, she begs me to take her back and starts being crazy. I’m 100 % sure I don’t want to have anything more with her, but I would like to know what is the best way to deal with such behaviour.