My gf and i cheated a lot im very hurt she wants me back what should i do?

Hey im alekxandar im 18 and i dont know if i shold get back with my ex its complicated story.
I was a guy who is kinda a **** boy, never go in relationships, constantly **** over girls, had a lot of gfs but none of them lasted more than a month. Then decided to try out how its in a relationship. I met this girl at the beggining of the school year 2 years younger than me, she was very warm and positive kinda seemed innocent. We hit it off very well i was very happy, then at around 2 and a half months of the relationship she cheated on me with her friend it was just a kiss and nothing else, she told me about it right after it happend and said she didnt even wanted it but she was crying over a fight we had he saw her and thought we were over she was very drunk (she really rarely drinks ) and in the morning she didnt even remeber it. We were broken up for few days then got back together. After we hit 4 months she found out that i had another gf for 2 months and that i was dating them both at the same time, i had to choose so i chose the other girl, at this point she told me that she was ******* her ex the whole time (but she didnt leave me because he didnt want her, he was in just for the sex and he told her that, they never were in a relationship before that, cause of the same thing he didnt want her he just wanted the sex and she was in love with him very much so she let him do anything, she told me he never treated her right and was constantly with other girls hiding her in the back). After me realising that i made a mistake and i wanted her back we got back together and we promised that we wouldnt cheat again. After a week into the relrationship i couldnt look at her knowing she had done that, and knowing that she is with me only because her lover dumped her and told her that he doesnt want sex from her anymore and that he doesnt wanna see her again so I dummped her again. After a week she texts me and tells me she wants me back begging me to come back to her she said she would do anything just so we can be together our agreement was she sends locations and snaps every 30 mins and i can go with other girls but after a while that i should commit to only her. I was very much in love with her so we talked about marrige and children (after the school year she will have to go abroad for a year we decided that we will do long distance and that we will buy very expensive rings so we r engaged). Then i found out that she texted the guy she was cheating with inviting him to a movie on valentines day (we were broken up on valentines day but before that break up she told me that she has no desire for him but asking him on a date on valenitnes day says otherwise). maybe 2 weeks before valentines day she aksed me if she could messege him so she could take her phone case back i told her okay they saw eachother and she told nothing had happened then, but while she was drunk few days ago she told me that she wanted to **** him that day but there was no place for it. I broke up with her and after that she calls me crying that she wanted me back, that she loved me very much, that she wanted to be my wife and have my children begging me to stay with her. I broke up anyways. And now after a week she texts me again telling me she wants me back.
Im very confused of what should i do i even read her text messeges with her friend in which she says she never expected to fall for me but now she thinks she loves me (and these texts were from way before maybe 2 months after we met ).
I dont wanna be with her as her second option just because she cant have the lover, but she says that she loves me, idk what to do.