The love of my life is thinking I'm not going to stick around - how can i make him believe me?

This is not going to be easy on either of you. He is thinking you are seeing other people because he can't see what you are doing. The mind plays tricks and you feel desperate. Connecting, communicating, visiting, talking on the phone, writing... it's all you can do. Do as much as you can and hope for the best. You might do everything right, never run around and he still might not come around. Good luck!