How to get over trust issues?

All of my relationships in the past were bad, and my current one has had its downs that made me lose my trust for him. Also, we are long distance because he is in the service. Yesterday, we got into an argument where I told him I don't know if I can be in the relationship anymore and I guess it pushed him away. He told me today that he can't live everyday thinking that I'm going to leave him, but I can't help but have all these negative thoughts that make my anxiety go through the roof. He told me that he's working on himself everyday to fix the mistakes that he has made in the past, and that I need to work on myself.. But I have no idea how I can get over these trust issues. 😔😪 I don't want to lose him, but I don't know how to fix myself....