You basically answered your own question. You felt comfortable with him, he was nice, you had FUN. Guess what? You're describing a friend! You've had sex so that bumps it up to describing a friend with benefits.

You also don't sound like you were really physically attracted to him. Ok, he wasn't hideous but the wrinkles and weight turned you off. Everyone wants to believe that "beauty" is "on the inside" but the truth is that for most people they need to have some physical attraction there. I'm far from a superficial snob but I do the same thing with men. I had sparks with the last guy but the fact that he was balding in his 30's was a turn off for me. (well there were other issues) I guess maybe somewhere deep down I want to "grow old" with someone and not get with someone that already looks old.

Regardless of what "type" of guy it is; whether a "nice guy" or "bad boy"..the physical and emotional chemistry has to be there. In your case, it wasn't. If you were in "love" with the bad boys, could it be because you knew it wouldn't last and just enjoyed them in the moment? Was Mr. Nice Guy too hard to love because it would hurt more if he dumped you?

As for "learning to love"..I'm definitely no expert. But my opinion is that if you can't love because you have so many walls built up and are scared of love and of getting hurt..then I guess you could "learn to love" by opening up more. But in the end I think if it were real "love" then the right person would magically break down the walls anyway. Speaking for myself in general here, not saying this is you.