Lol, I agree the doctor sounds rather more exciting.
It is not the other guy's fault. He will find someone. But I know how you feel. When an elevator door closes, and someone doesn't make it in, I always feel like it's MY fault. We're powerful people, aren't we, us people who are responsible for everyone else's feelings?

Maybe you could just tell him you really like him, and he's a great guy, but you found someone from your background (or something the guy has no control over) and really hit it off with them, but you hope you can stay friends as you really like his personality. No way he can feel bad from that!