What do you do when a long lost love comes back in your life while you are in a relationship?

If you aren't married and you feel you want to see where meeting your lost love will take you then just be honest with your resent boyfriend and even though it will hurt him it's better than cheating on him. Try to remember why you did lose your love and if he wasn't good to you or was arrogant and just left you flat then I'd consider keeping the guy you have. Old habits die hard!