Most Helpful Guy
The past might not dictate the future, but patterns do generally repeat themselves. If its been on/off again for the duration of the relationship, why would this ever change? Short of experiencing a moment of clarity, which typically happens in the form of definitive separation, it's very unlikely that such a relationship would work out.
Most Helpful Girl
Well I believe that we are in this world to be happy, and I don't accept less than that. If your friend is happy with this guy or if she thinks she is, doesn't matter how hard you try to explain to her that his not for her, she won't see it until she wants it. I have a friend like that and every time they breakup she agrees with me and apparently she forgets it all and comes back to him. So, you just tell her how good she is and that she needs someone to make her happy, not miserable. but really, there is not much to do until she gets fed up with the whole situation.