Reading about your j thing, my first big crush in college, we dated for a month and I actual broke it off, because it was painfully obvious I liked him so much more than he liked me, I was trying to save myself some future heartache. It still took me a long time to get completely over him.Anyways what was funny he then started dating someone from another college. Who happened to have the same hair color (and general haircut), same major, and even the same first name as me. I guess it could be coincidence.
Yes! I've done that, too! Twice, I was with guys who I really, really liked, but it was painfully obvious they weren't as into me. Both would have been happy to have sex, though - but although I was really into them, I didn't sleep with either of them, because it would have ended badly for me, emotionally.
Weird story about the guy going with your doppelganger! Maybe you shocked him with the dumping, and you're the one who got away!