It sounds like a difficult situation for you. He ma really care for you, but he obviously can't truly pursue those feelings until he resolves his past relationship. My thoughts are if you wish to have any chance at a future with him, you tell him he needs to find closure with his former girlfriend before moving forward with you. If he can't do that you are wasting your time. He may eventually come around but I'm not sure it's worth it for you. Does that make sense to you? Let me know if you have questions. I want to be a help.
That does put a whole different spin on it. It sounds to me that you guys need to attend couples counseling. I am figuring he will resist this thought he seems to want to stay with you though. Basically, give him an ultimatum. Either he works toward making things better for you move out until he does. The key is, if you say that you're going to do this, you need to do it. Honestly, it does not sound hopeless to me. It does need work though.
Then I would say you're insecurity is well based. He.obviiously has feelings to her. I'm sorry, but you are his security blanket. If you are ok with a short term relationship where you are 2nd then this is for you. I don't thibkbyoubeabt that though. My advice would be to call it off. If you are available when he gets over her, then make a decision then. He definitely is not ready now though.