That seems like a problem, I really feel compassion with you. Well first of all i think it´s important that you tell someone. Maybe even start with her, I know she its only 13 but i think she will understand your problem. And then after a while you can start mention to him, if I where in his situation I would totally understand. Because it´s nothing wrong to be in love with a a minor. Always remember "Love has no limits". And if you guys are best friend I´m sure he would´t make such a big deal of it, thats what best friends are for, right?
That's a really good answer!! :D
SvaraRadera