I got a brother that's in a long distance relationship, however it's only a 4 hour drive for them, sometimes 3 depending on traffic, they see each other almost every weekend, taking turns as to who drives to each others' location. They make it work, guess they really love each other.
But in your case, 12 hours is tough man. Plus, only seeing her for a few days a year is not good, especially if you're on the sauce, that sky high libido and no one to bestow that upon, that shit is hard. Maybe if you're natural all year you might be able to control the sexual urges and be faithful.
All around just not the best situation for you, and phone sex is not enough, wtf is this, Middle school?