I caught my (ex) boyfriend on a singles meetup group. I ended the relationship and didn't even give him a chance to explain. I been down this road multiple times with my previous boyfriends, so I wasn't interested in his excuse. We have been together almost 4 years. I ended up getting off his phone plan and he told me that he loves me dearly. What are your thoughts? If I get back together with him, how am I supposed to trust him? How do I make him respect me and focus on me and not other girls?
Set some clear boundaries and tell him exactly what he needs to do to appease you in order to make you trust in him again. Tell him what kind of behavior is taboo and make it clear that if these conditions are violated, then there can no longer be any trust between the two of you and therefore the relationship needs to end.
Furthermore, you need to go for relationship counseling and he needs to agree to go together with you.
Source would be my personal writings on the subject: http://www.relationshippsychology.com/cheating/cheaters-caught-in-the-act
I wouldn't take him back. You deserve better.
Frankly, you called the right shot in the first place. If he didn't make you his priority then, why will he change now.
Just because he's been caught doesn't mean he will accept any boundaries now and in the future. His actions have spoken and it doesn't matter if you are at fault or he is or both of you are, regardless, if he loved you dearly after 4 years, he would be true to you in every sense.
You said you didn't give him a chance to explain. Why not?
You said he was "on" a site. Was he participating in exchanging info, etc.?
Or just looking at who's was on there?
You are going to have to decide if you want to see him again (notice I didn't say "go back")
How old are you two?