Rational or Jealous? Is it well founded?

Am I being paranoid? My boyfriend has a female "friend" (actually, he has plenty, but one in specific scares me). Right off the bat, when we first started dating, she gave him a shirt and said that she had purchased it for an ex, but since they had broken up, he could have it. It is an expensive shirt. I have heard from another friend of his that he use to like her. He went to a photo shoot with her, from location to location, that took up 2.5 hours. He is escorting her to her grad. I don't know, it seems like they are more than just friends to me... what do you think?