TL/DR: On the edge of keeping/breaking up GF, don't know what to do

Hi guys, I'm a 19 y/o male. When I was plating, I found an 18 year old girl which was good gf material (virgin, conservative family, strong dad, knows how to cook, pretty smart and a great ass). I plated her first as well, but later decided I wanted to try the whole LTR thing just to see what would happen. This is my first post-TRP LTR and so far things were going great.

When I saw her the second time, she invited me over to her house (her parents were away). I slept there, but we couldn't fuck because she was on her period. She was very horny, we showered together and stuff like that.

Shortly after we had sex a couple of times, but I was still plating her. I was thinking of LTR'ing her. She then went to a party, got very drunk. My gut was telling me something was wrong, so I asked her if she kissed a guy that night or anything, to which she answered no.

Fast forward 3 months, our LTR starts. Lots of sex, great girl. Now 2 weeks ago, I learned that she did indeed kiss someone that night on the party. I was devastated that she lied to me so easily and that she completely "forgot" about it. I was kinda glad she finally told me, but my trust was pretty much gone.

Now comes the monkey out of the sleeve, she told me earlier that she sucked of a dude once when she very drunk. I was kinda ok with this, because I thought it happened all before me. Mind you, this was almost all sexual contact she had except for getting fingered by 2 guys. But this week she told me that she reminded that the suckening all happened on the fucking night after I first came to sleep over.

Obviously this makes a lot of sense. I made her so horny that day that she just had to lose it, even to some other dude. Same for when she kissed the dude at the party, because I fucked her 2 days prior. I see this pattern that when I make girls horny, they usually end up doing something with someone else once I'm gone. I also did not tell her that I wasn't okay with her not doing things with other guys.

I have only felt so desperate three times in my life, over the same girl. I do not know what to respond to this. I don't want a slut as GF. But I only told her a lot later than the kiss with that other dude that I was not ok with her doing these things. It just bothers me so much, I don't know what to do. After I first came sleeping over she was hinting a lot about wanting more than just fuckbuddies, still she sucked of some dude and kissed someone else.

I strongly believe that this girl will stay loyal to me for at least a year, she does everything for me and is terrified to lose me.

The doubt is fucking killing me, I woke up at fucking midnight to write this. Idk what to do, this girl is really great but idk if I can live with this now that I know it. Can someone please give their guidance about this problem?