Lust is powerful and it's easy to feel totally consumed and out of control. I have been in similar situations and it's a horrible drug being so drawn to someone that they occupy your every thought, it's physically draining and painful.
But - you are fuelling it. He is an addiction. Rationally you know there is not a long term happy future with both these men in your life, you only stand to cause destruction to two families if you don't stop now.
Make a choice. The same one you made last time - your husband - and truly expel all aspects of OM from your life. It will take time to stop yearning for OM, really it will. Yes, it's easy to name call and say what you are doing is mean and nasty and I'll judged, but deep down you know that. You first need to get over this and make your choice.
If the choice is OM, it's highly likely it's a temporary fling. Would he really leave his wife, would you play happily families with him and your children? Would you be his OW for the next X years chapter?
Rid yourself, stay in the pain room and get over it. You know you can't have both or you wouldn't have posted for advice.
When I was in this sort of situation I didn't have kids. Now, I find it hard to imagine as I suspected I would be totally driven by how my children would feel if their mother put their father in this cruel, sad, powerless situation. Please choose wisely, and be strong. Getting over this either alone or with RL support from a friend or your DH will take time and a great deal of strength.
Good luck.