What am I to do and is he ceating on me?

I think that this more of a question of whether or not you trust your boyfriend. Other than talking about his friend, who I assume he’s close to, has he ever given you any other reason to doubt him? I can completely understand where you’re coming from with this, but I think that by constantly going off on him about her you’re showing him that you DON’T specifically trust him. So, I can see why it upsets him as well. I’m sure you wouldn’t be happy if your boyfriend did the same to you about your friends, right? And if he does, just think about how much it annoys you (which I assume it would do regardless).

You’ve told your boyfriend how you feel (which is important) and I think that he tried to reassure you that there’s nothing to worry about by mentioning that he’s with YOU, and not her. They are friends and I think that you should try to trust him a little more. If you don’t, you’ll only push him away with this kind of behavior. Don’t let jealousy ruin your relationship.