How Do I get Trust Back after bf kisses, and flirts..

When I first started dating my boyfriend a year and a half ago everything was amazing, he treated me like a princess and cared sooo much about me. Except I felt he cared about others a little too much too( he's a very friendly guy) but sometimes it would come off as flirting to me, and it really bothered me.
I didn't tell him about it since I didn't want to be known as the 'jealous' girlfriend.

Then it started getting worse since there would be pictures online of him at parties with other girls and stuff and it bothered me and I cried myself to sleep since I didn't want to tell him it bothered me, or even worse when he posted photos of other girls and never any of me..then it was getting worse since we went to a party together with our friends then a few people started playing spin the bottle and he went and started kissing another girl RIGHT IN FRONT OF ME. He knew i was upset then and stopped.
Long story short after that he stopped drinking, partying hanging out with people since I was about to break up with him. I didn't want him to stop doing any of that stuff I just didn't want him to cheat on me...I feel bad since he rarely does anything anymore since he says he doesn't feel like doing anything with them but I know it's because of me...I just want him to hang out with his friends and have a good time and drink if he wants BUT makes the right choices except he won't drink anymore at all...I feel like I should of broken up with him a while ago but he treats me soooo good and we have the same humour, and always have a good time( when I don't think of the bad times) when I do I always get depressed and sad but he always tries to make me feel better. Lately though there is nothing to cheer me up...I'm just to upset about the past. Any thoughts on what I should do?? I REALLY do NOT wanna break up with him but I just want to be able to trust him again, since i haven't in like a year.