My BF kissed another girl

Hey girls.. I’m completely down, crying all day and don’t know what to do.. I have the sweetest boyfriend ever - he takes care after me a lot, prepares me breakfasts, helps me to change to bed when I’m too tired.. recently (well - 3 days ago), we had our 1 year anniversary.. He is my first boyfriend, my first kiss and we’ve lost virginity to each other.. he has that sweet, innocent and shy type of personality, so you wouldn’t expect that from him.. but few hours ago, he admitted, that he kissed a girl last Friday. He regrets that a lot.. really, he has been crying way more than I am.. Well, he was drunk and he doesn’t feel anything for her - they didn’t even hug, hold each other’s hands.. just kissed - but multiple times in that night.. I don’t take it as cheating, just because it was ‘just’ a kiss + alcohol, no feelings.. but I feel pain, I’m hurt so much. That evening, he even sleeped in my house, I took care after him that night, when he couldn’t come home by himself and so the next day when he was feeling really sick. That night, I wated for him till almost 3 o’clock to go back, prepared him dinner and I was afraid if he’s okay.. there are a lot of small disagreements, that we have right now and I don’t know, what to do.. I’m not mad, I’m just really upset.. I can’t kiss him.. I just always imagine him and his lips holding tight on another girl.. Those soft lips were my privilege, I was supposed to be the only one that he gives a kiss to, not another girl.. so, what shall I do? I wouldn’t be able to find someone like him any time again but I’m not sure if I can really go back with that.. but it’s probably just nothing, right? No big deal.. but I don’t know, it hurts a lot

!!! EDIT: well, he has showed me the messages with the girl that they were sending to each other a couple of days after.. there was written, that he really doesn’t remember anything and that he doesn’t know why he did it and why he continued.. but in the middle of this kissing session, she asked him if he’s in a relationship.. he said yes..so she said that they should stop, but he said no, that he wants a lot to kiss her, he needs to and can’t stop (he couldn’t even go home on time because he just kept kissing her) and he won’t and doesn’t regret anything (he said that in that moment).. but OMG.. that hurts so so so much so badly..