u/Aromatic-Struggle-47

I’ve been in a relationship for 4 years. I just found out he had a one night stand with a girl and I also found 2 chats on his phone with other women. He hooked up with the girl in the beginning of May but he picked up my engagement ring at the end of that month. I have no clue how someone can do something like that and still go through with an engagement. This is all new to me and I need advice on how I should move. I know he was planning on popping the big question but I feel conflicted now. Is there room for repair or should I just leave?