One of the biggest ways to fail is to not be yourself and pretend to be something you're not. I don't know you, but you say you're a nice guy. Thats what you are. What you need to understand is that that isn't the only thing you are.

Attracting a mate, you have to be at the top of your game. Not as faggot player, just at your best. If you have no confidence in yourself, it will show. I'm pretty sure with how you feel, you even realise it. Girls notice this. Hell, anyone does. Body language is universal.

Don't give up on being nice, just do so in moderation. What sort of things do you do that gets you classed as a 'nice guy'?