How would you discourage a young man's romantic interest?

I have this friend who is absolutely smitten with me. This is becoming quite a problem because I feel as if I cannot really be friends anymore with him. It’s not that I don’t want to be friends with him, quite the opposite. He’s very interesting, a good guy, interested in many of the same things I am and he works at a gaming store I frequent. Truthfully, though, I do not go there very much anymore and never alone because I am not interested in him. I have a boyfriend, whom this young man knows, and he still makes me uncomfortable with his interest.

Now, the real problem is that his “advances” are not so active as to draw attention and if he hadn’t told me that he thinks I “would make a good girlfriend if things with Bob go south” direct quote I wouldn’t even notice now. However, sometimes he’ll text me with something perfectly normal but then add something like “I miss you” at the end. The other day, after not having seen him or contacted him in any way for more than a month, I saw him again. I figured a month of no contact would shake any crush this young man had and, well, I believe I was mistaken. When my friends and I went to leave, he hugged me a perfectly normal act between two friends and he was reluctant to let go a not so normal act. And he has this way of looking at me, that sort of soft, love-sick look you get when you have a decided romantic interest in someone, even when my boyfriend is around.

To get to my actual question: how can I stop him from liking me in this way? I would very much like to remain friends with him and I do not want to stop going to this gaming store and since he works every day it is open, I can’t simply avoid him by going on his off days. I do not think he would try to do anything sexual and after I made it clear that I am happy with my boyfriend, he never mentioned that he and I should have sex or anything of that nature. It’s just that I don’t want to be always on my guard when around him, which I already do enough.