help understand

I have this amazing boyfriend right now but I always feel like I'm losing him when he said I will never lose him so I'm always worried something bad might happen. We're talking about moving into an apartment together and going to college(different colleges) but in the same area. But we both scared we both want to last and he talks about a future with me all the time. I don't understand why I am so worried all the time.what can I do? I use to be in a bad relationship and I always got cheated on but he's completely different from all the other guys. I don't want to push him away but I always think he's leaving and I get worried. Anything to help?