How do I convince my friend that I won't change, and our friendship won't change, when I go to college?

My friend and I are very, very close, I would go as far as to call him my soul-mate. We're not romantically together, as he has been with his girlfriend for six years now (he's a few years older than me.) He's convinced that the special friendship and understanding we have of one another will change when I move to college. He says there is so much of the world that I haven't seen yet, and that when I'm welcomed to this new world, I'll forget all about him and the interests we share and the things we do together. We won't be able to see each other much, because he'll be living with his girlfriend, and I'll be at college. I try to tell him that things won't change and I'll IM him in the evenings like we always do, and I'll speak to him on the phone and do all the things we always have done, but he just says "it won't be like that." He's a very insecure person, he always has been, and I know that it would hurt him deeply if I move to college and forget about him, just like I would hurt if it was the other way around. I don't want to change, I don't want to give up on my friend and become a different person, I still want to be close to him and share the close friendship we always have shared. But I'm frightened these next few years are going to be difficult, and everything will end in tears. Any advice or help would be appreciated. Thank you.