Relationship anxiety

I seem to have a never ending reel of things to worry about. Usually about my relationship. I know I have nothing to be anxious about. We have a house together, get on amazingly, talk about our future all the time. Yet I always have constant niggling stresses about situations I'm pretty sure are just in my head. He copes with it well, I just am so scared it will put a wedge between us and he'll get fed up. And then all my anxieties will come true... He will find someone else, want to move back with his parents, ditch me, never speak to me again etc. I just don't know how to keep my thoughts and worries under control.