I don't know what to do

I don't know what to do. I have no reason to be unhappy with life, but I've had one consistent 'issue' since I was a young child.
I suppose it's not that I see it as a problem/issue. It's just that I don't know what to do. Since I was 11 or 12, I've fantasized about being a girl. I've bought makeup, worn women's clothes, and I constantly think about dressing up. I've just now gotten out on my own, and since the urges have increased. My family would shun me if I told them. My friends would back away, and I would lose my girlfriend, who I love and care for very much. But every time I look in the mirror I wish I was a girl. I wish I could be feminine. And then afterwords I scorn myself for such thoughts because I feel like I'm doing wrong. I wish I could figure it out.