He doesn't want to marry me.

My boyfriend and I have been together for 2 and a half years. Marriage and children have come up a lot it’s becoming more important to me. I live for the day that my man makes this big romantic proposal because I know that we’re so in love… but, he tells me that the only thing that is holding him back from proposing to me is my jealousy. I don’t get it though. I’m not that jealous and I think that once he proposed, I’d feel less insecure. I’d feel like he really does want to be with me forever. He always says that he doesn’t want to marry me for that reason and that reason only. I’m sure a lot of people know how I feel and they know that it’s not easy to stop jealousy because believe me… I wish I could stop being jealous. Am I wasting my time here? If I know it’s too hard for me to change, should the relationship just be over? I don’t know what to do here… I’m in a relationship and we love each other to death but I don’t see it going anywhere right now. Please help.