Is he cheating or am I paranoid?

I have been with my boyfriend since February. We were inseparable from the beginning. Now we are living together. Things have been going well up until recently. I lost my job a few months ago. Things have been a little more stress full but not all that bad. He tolled me when we first started dating that he had a thing with this girl he went to school with. He said that when he tolled her that it was over she gave him a very hard time. She did not take the news very well. He still has classes with her, every once in a while she will call him asking a question about school work. They never are on the phone very long. They both are really into WOW. She went to a convention in California and brought him back a t-shirt and a key chain. We talked and he stated that he asked her to bring something back since he could not go. When I tolled him that I think she may have additional attentions of getting back with him, he asked if I trusted him. Of course I said yes. I think I do. I don’t want to tell him that I have some doubt. Ever since then I am feeling very threatened by her. I feel that their friendship has gotten stronger and maybe he regrets not being with her. Recently I noticed that he can’t look at me very long during conversations. Am I just paranoid? Should I say something? If I should how do I say it?