Leave them alone.
I'm saying this as a guy who has friend girls who I would LOVE to be with if it wasn't for their bfs. BUT, I will never pursue anything with them because I wouldn't want anyone ever to leave their partner for me. It's just wrong. I would never trust them.
Don't cry, don't regret and don't blame
Weak find the whip, willing find freedom
Towards the sun, carry your name
In warm hands you are given
Ask the wind for the way
Uncertainty's gone, your path will unravel
Accept all as it is and do not blame
God or the Devil
~Born to Live - Mavrik~