hey, I just need someone to talk to, it's a bit of a long story but yesterday morning this random man messaged me saying he's just found out his girlfriend is cheating on him with my boyfriend, saying that my bf sent dick pics to her and asked for pictures in return, I showed my boyfriend and we just laughed at it, i said 'isn't it great how not for a split second did I believe you could do that' and we went about our day. he started to get itchy revealing bit by bit that he actually knew the girl, he swore to my face that he didn't do all that stuff. I gave him chances tell me the truth and he finally told me that this girl messaged him saying she thought he was fit all those years ago (they grew up together) and asked if he would've fucked her back then to which he replied yes. he promised he never sent pictures. but I rang the girl and she said it was all true and that he'd sent dick pics. he confessed to it all. I'm so heartbroken. we've been together for 3 years and I'm only 18. I just don't know if I'm over reacting or what to do. he said it was a moment of weakness that lasted an hour and that he was just giving in to the attention (of which I give him plenty) I have only ever been good to him and he has been the best most loving boyfriend in the world. he feels so so guilty. he told me he also said he 'would have been the biggest cock' she's ever had and it just lingers with me. it makes me feel sick because that's not him at all. what should I do?

update... I have severe depression and I have no where else to go, we have lived together for most of our relationship, we have a home together, he wants babies with me and to marry me, he broke down in tears, he said he can't go on without me and I love him so fucking much. i know i should leave but I'm not strong enough to.