me, my boyfriend and his friends

hi everybody. so, we are dating for a year and half. and almost all this time we spent together. we really love each other and have fun. but...

from the start of our relationships I've asked for sincerity. and I've explained that I need to trust a person I love. but from the beginning it was something wrong: I was working all the days long and he was sleeping at that time and hanging out with his friends. I don't like that company, some guys are ok, but most of them are people who are interested only into ways of how to get drunk and to smoke. so every time he meets his friends, we have a quarrel. and I'd like him to be with his friends but I just can't stand this!
There were a lot of cases: when "his friends phoned some girls he doesn't even know from this cell phone" (c) and they were writing to him a day after, when he was with me; when he and those his friends were going to the sea, met his ex and her friends and stayed at night, were swimming naked while I was not with him, I was working; when he was hanging out with those friends and their girl they treated as a friend and he was dancing with her, and again, I wasn't there…. and after a year of relationships I've founded that the girl I was writing about was not just a friend and he had a sex with her (when we were not together). and he didn't tell me anything and continued hanging out with her. he said that he was trying to save me from all these things. but it's so unfair! don't you think so?

so when we are together, mostly everything is ok. but I can't trust him when he's with those friends. they are just awful. I was trying to hang out with them but once we were sitting in a restaurant, and they joined us, they were drunk and were swearing and I had to listen to all this… they can't be nice people. and they have no girlfriends… we are something different. but we can't be only together all the time. and he has no other friends…

He isn't behaving like someone who is in a committed relationship. He's not trustworthy, you need sincerity, he apparently wants to have fun with his friends, why continue on?

How did you find out about this skinny dipping incident?

it was at the beginning of our relationships. and he told me once, in about a month or two after, like it was just a random fact. and he said that he realizes it was a bad idea. but at that time he doesn't thought about it.
he seems to love me. but at the same time he seems to be a person who can't be trustworthy and who always will be cheating at these moments just because he doesn't realize how awful it is for me.

sometimes I just wonder what's wrong with me, and maybe it's just my problem. maybe all guys are cheating and just don't show this. or it's such a big problem to stop hanging out at one time. he's only 23, like me. maybe that's the problem for mature relationships.

thanks for your answer!