Boyfriend kissed another girl

Hi.
Background: My bf and I have been together for three years and until the past couple of months things were going really well. He used to treat me so well; take me out everywhere. Literally the only problem I had with our relationship back then was that he would break contact as soon as something more important got in the way (and I'm talking months of no or at least very little contact). We moved to separate unis and suddenly things began to change, he stopped talking to me again and stopped making an effort, I'd ask him to change and nothing would change. It was like he had become a completely different person, he stopped telling me "I love you" (claiming his friends thought it was tacky, with no discussion with me about it) and stopped complementing me at all. But then continued to complement his friends (girls), saying that he was just raising their self-esteem.

I kept asking him whether he really wanted this and he's always say yes of course I do and eventually he started to get annoyed at me asking, because he was unable to see that his actions were giving me such mixed messages.

Eventually we stop arguing and decide to just act like nothing was wrong and talk like normal and after a few days of this things were going good until he told me that he had kissed another girl when drunk. I don't really know where to go from here really? I know he was drunk but honestly, I'm not sure if that's even a valid excuse because if someone he didn't like had kissed him then he would have pushed them away.

But how am I supposed to trust him now, first he kisses someone else, next he'll sleep with someone else you know?

Hi.
Background: My bf and I have been together for three years and until the past couple of months things were going really well. He used to treat me so well; take me out everywhere. Literally the only problem I had with our relationship back then was that he would break contact as soon as something more important got in the way (and I'm talking months of no or at least very little contact). We moved to separate unis and suddenly things began to change, he stopped talking to me again and stopped making an effort, I'd ask him to change and nothing would change. It was like he had become a completely different person, he stopped telling me "I love you" (claiming his friends thought it was tacky, with no discussion with me about it) and stopped complementing me at all. But then continued to complement his friends (girls), saying that he was just raising their self-esteem.

I kept asking him whether he really wanted this and he's always say yes of course I do and eventually he started to get annoyed at me asking, because he was unable to see that his actions were giving me such mixed messages.

Eventually we stop arguing and decide to just act like nothing was wrong and talk like normal and after a few days of this things were going good until he told me that he had kissed another girl when drunk. I don't really know where to go from here really? I know he was drunk but honestly, I'm not sure if that's even a valid excuse because if someone he didn't like had kissed him then he would have pushed them away.

But how am I supposed to trust him now, first he kisses someone else, next he'll sleep with someone else you know?

he stopped telling me "I love you" (claiming his friends thought it was tacky, with no discussion with me about it)