Yes, but it depends on what they do. They have to make amends like their life depends on it. They have to create a miracle that changes their own life and the lives of those around them. By this, they show they are strong enough to leave their great sin behind.
The great sin, no matter what the specific, physical action, is one of allowing temptation to control them. The temptation can be one of lust, rage or any other dark emotion or physical distraction.
Sometimes, though, it is good to give them some distance so they can find the strength and not to use yourself or others as a crutch.
Always give unconditional love, but wisely. Sometimes it is tough love, sometimes it is distant love, but it remains strong love, nonetheless. By "love," I don't mean physical, biochemical feeling or reaction to stimuli; I'm talking about unselfish caring and compassion despite anything they do.
By all means leave, if that is the best thing to do. And don't stay out of habit or misguided feelings based on memories. What you do can help them change if done wisely.