Idk if I should keep him or let go?

[Whitney]

Ok so my best friends neighbor and I are dating and I went to a party with him and he mentioned something he saw on twitter (he doesn't have a fb) so I'm like hmmm I'll look him up on twitter. I found out that his old account was closed but someone else had mentioned his account in a post so I clIcked her name. In her bio it said I am in love with "..." (I won't name names) and I saw lots of posts showing that he was and still is dating her. She had pictures proving it from football games ect. For sure I know that they got together about 4 days before him and I did. It says they've been together 3 years but idk if that's what she was talking about. Anyway.im going to see him tomarrow and talk to him and her. Point is that idk if I want to completely dump him or keep him. I know once a cheater always a cheater, but my dad was one and now he is committed and married. A part of me wants to leave him but he also has made me very happy and besies the obvious he's perfect likes a lot of the same things I do and we get a long great. Idk what to do please help!!