I think the first step here would be to realize that you do have a relationship with this girl, whether you want to or not, whether you're comfortable with telling your friends you are or not. You have some deep feelings for her. You can't get her out of your mind. You two are together.
Are you sure, among all your friends you've grouped as "homophobic," that there isn't one that you could talk to about this? I know that sometimes I imagine people's reactions and it freaks me out, but they turn out to not mind too much at all. It really, really helps to have someone in real life, who knows you well, that you can bounce your feelings off of. (We're here for you, of course, but sometimes it can be easier with people you already know.)
I don't think you need to cut her out of your life. You still get to see each other, and you still talk--there's no reason this can't exist as a long-distance relationship, is there? I think what you're missing here is some support other than her, and even if you don't tell your family, it might be worth telling someone--a friend, a teacher, a counselor--so you don't have to keep this all bottled up inside. It sounds like the secret is what's tearing you apart; your girl is just fine, right, and you love her to pieces, but keeping that a secret is tiring and hard to do.
Kissing girls in English at the back of the stairs, you're a honey with a following of innocent boys, they never know it because you never show it..." - Belle and Sebastian