I cant say your homosexual because you havent stated an attraction to males. If thats not the case then really something else is going on her and it probably has alot to do with how you view yourself. I know alot of guys who frequently get turned down "for being too nice" aand get the "I just see you as a friend" line. After awhile, surely this can weigh on your self-esteem and your ability to interact with other females because you automatically have the notion that your not good enough. Hence, you've stopped trying all together. You shouldnt give up though. Pay attention to the kind of girls your friends always bring around...Perhaps their far too immature for you if they still think that being too nice is actually a bad quality in a guy. Also, look at how your guy friends treat them. They wine them and flirt with them maybe only so that they'd wind up in bed with them. Is that the kind of girl you'd really want anyway?
First, you need to work on yourself before you can converse with girls well. When you build about a better confidence and self-esteem things should change where you'll get better at being social with the ladies. In the meantime, dont be a hermit. No matter how nervous you may get when girls are about, dont exclude yourself because then your not helping yourself at all.
You can be friends with these girls, but you dont have to act like a womanizer to obtain their interest. From the sounds of it, you could careless if their interested or not, the point is being anti-social with the opposite sex doesnt make you appealing whatsoevere to anyone else. If you can use them to build better social skills you'll be in a better position with a girl you would normally go for. Maybe you'll even be able to approach her on your own.
You dont want or need a girl who just wants to party or hook up. A girl who accepts you for who you really are and is respectful. grateful, and apprecaitive of your kindness is more your type. Only a mature girl will notice this and not see your actions as "too nice" because a real women knows..theres no such thing!