If you truly feel that your marriage is over and that you have tried everything to make your marriage have more passion and intimacy then what you are going to have to do is find closure within the marriage before getting involved deeper with this other man. If you go into a relationship without ending your marriage it will make things more complicated than they need to be. You have to be honest with your husband about the way that you feel and what you want to happen next. You never want to live your life with regrets but you also do not want to do something behind your husband's back because I believe there is such a thing as karma. Do not open your heart to someone else until your marriage is resolved and then when you are free and single then open your heart to someone else. Make sure that you have definitely tried everything when it comes to your marriage so that you can leave with a clear conscience and knowing that you tried everything.