No, "I said so" is an improper response to an argument, especially when you need to prove a point. Consider responding with a logical or factual statement, and backup your statement with a reputable...
He probably is nervous and doesn't want to get rejected even if he knows you like him. If you really want to go out with him that bad, ask him out. The worst he can do is say no.
As a woman myself, I will admit woman can be hard to understand sometimes. The question is ... have you ever really listened to what you girlfriend is saying? I doubt it, because most men don't. It's...