Afraid and scared

Iaky so let me start out by saying my boyfriend is an amazing guy and I love him so much we've been together for almost 2 years (1 year and 10months) we have the best relationship no matter what happens we always work everything out and we even talk about getting married having a family together and stuff and I wanna spend the rest of my life with him but I'm so afraid I'm going to lose him and he tells me all the time I won't and I believe but I still feel like I will lose him and it scares me I never want that to happen how do I make this feeling go away