What do you do when you want a man that has a girlfriend?

okay so this is the predicament i am in...i have found my true other half but he has a girlfriend....they are always arguin and he dont seem happy with her....he said he loves talkin to me and he wants me but i dont know what to do....i want him too but what about his gf.....i mean we make each other happy....he knows how i feel and we have established a friendship....but i cant have him yet...he stays over 3000 miles away.. :(...