How do i get over being jealous of my bf's ex? or is my jealousy founded?

my bf and i started seeing each other two years ago and he moved across a few states to be with me. we moved to fast and things ended badly after 4 months, and he moved back to where he came from, back into the arms of the woman he left to be with me. they have at least ten years of ups and downs together. just recently we started talking again, working things out and healing over the past, and hes no longer in a serious relationship w her any more, but they are still realy good friends. he goes over to her place at least once a week, and they cook dinner together and sit and watch their favorite tv shows together. he stays out w her untill the wee hours of the morning, but tells me that they are strickly platonic. he hasnt told her that we are getting back together bc he needs her help w taking him to do laundry bc he doesnt have a car, and knows that when she finds out, she wont ever want to talk to him again. he has told me that she asks him from time to time if she can "spend the night". he says he tells her no, and that they have no physical contact. im having a problem with her and her thoughts. since im not in the same state with him, i get jealous over how much time he spends with her when hes supposed to be mine. he tells me that if i trust him that i wouldnt feel jealous, but he left me and went back to her in the begining. im planning on moving to where he is to be with him, but my jealousy is making me afraid to move up there for fear that he mite leave me again and be with her since he values their "friendship" so much. am i justified in feeling this way? and if not, how can i cope?