He thinks I'm going to cheat...

So to give you a little background info, my boyfriend has been in some relationships where his girlfriend has cheated on him including his ex fiancé. I can understand him being scared of me cheating on him since girls have done it to him in the past but I just don't know how to prove it to him that I won't! I have more guy friends then girl friends, I always have because I just get along with guys better then girls sometimes. And one of my guy friends likes me but 1. I'm in a relationship 2. I don't like him at all. All I want is a friend not a guy who has a huge crush on me. So I can tell my boyfriend doesn't like that I hang out with my friend sometimes. My friend invited me to go to the beach with him this week and I told my SO about it and he said he was ok with it but then he said that I'm going to tell you the one thing I told my ex fiancé when we first started dating, "call me and break up with me before you cheat" and I just got so depressed when he said that...I texted him earlier saying that I will stop hanging out with my guy friends and stop talking to them on Xbox also. (I'm a huge Xbox gamer) and he hasn't responded so I really don't know what to do.