Is it normal that i'm scared to lose him?

When I was in high school, I really liked this boy, I've liked him for about 3 years now, but we didn't really talk a lot, and I was too scared to tell him I liked him. Then he got a girlfriend, I hated it, but in a weird way we became closer, we became like best friends, we always used to text each other and sit by each other in lessons, and have a laugh together and really enjoy each others company, but he told me he didn't like me in any other way than friends, his girlfriend hated us talking to each other, and the fact he took me to the prom made her mad!! Then we left school, and kept intouch, and about 3 months ago he split up with his girl friend, he told me why and what had happened and stuff and I was there for him and we started talking a lot more, and becoming closer, we went to the cinema together and each others houses and then about a month ago he told me he liked me and that he wanted to give things a go, so a month later were still together, I love him to pieces, he means the world to me but I'm so scared to lose him, I've liked him for so long, and I know I shouldn't feel this way because we're happy together, but I keep thinking I'm going to lose him and that he's going to go back to his ex girlfriend, and I wonder what I'd do without him! Is it normal to feel this way??