I need advice...

Recently, I started seeing My "first love" again after 5 years of not being together. We live in a small town so we would always run into each other and hangout once in a blue moon but never anything more until now. We started dating. Well, while we were apart, about two years ago, I had slept with one of his "friends" but really just an acquaintance to him. But before that one of my Best Friends had been hanging out with people he hungout with and ended up chilling at his house a few times I guess and he had tried to make a move on her(make out) and shit but she said no and nothing happened. She told me right away and everything. She's a good friend, but I just still can't seem to get past it.. I really plan to be with him for a long time and don't want to stress about if we to all hangout, how I would be uncomfortable. Has anybody been through this or can give me some tips on how to move past it? I know nothing happened but just the fact that he wanted to upsets me. 
Thanks.