This is the problem with the proverbial "nice guy", they need relationships. Instead of living for themselves and viewing women as sound additions to thier lives, they need a relationship. They are very attached to relationships, instead of having a good time.

That is why they'll get lines from women like: You are going to make a girl so happy one day, because ideally a girl would be enthralled to have a nice guy, but we all just want a real person who is attached to having a good time with some one they care about, instead of some one who needs a relationship. Men or women, for that matter.