Divegirl, you can give him up, and if you don't you will wish you had. There are many lives in the balance. Yourselves, spouses, children... so many lives being ruined by what you are doing. You have an emotional addiction to another man, and the way to fix that is to cut things off with him and have ZERO contact with him from this point onward. I promise you, your feelings for him will fade in a few weeks if you cut off all contact, and then you can deal with your own marriage.
The alternative? Ruining the lives of both families, "winning" for yourself a new man who you will never be able to trust (just as he will not be able to trust you), the hardships of broken families and bitter ex-families, damage to children who will carry their burdens into their adult lives and their own marriages, financial ruin, the ruin of your reputation, and most of all, a separation between you and the Lord that will be difficult to bridge.
This is not the answer, and God will never bless it. I am praying for you to make good choices that will glorify the Lord.
Divegirl... PLEASE listen to these wonderful people. In my own life, just within the last few days, I have been chronicling something very similar to what you are going through.
Read it here if you would like:
http://christianchat.com/christian-family-forum/79258-marriage-troubles-looking-strength.html
The "short and sweet" of my experience is this...
My wife and I found walls in our marriage.
She finds another man to be with for this last year is married WITH children.
I find out almost completely by accident while fixing her old phone she gave to one of our boys.
For the last week, it has been an absolute nightmare for me, trying my absolute best to seek God's help.
She has agreed to counseling, and we are now on the road to making repairs.
The very first thing I said to her was that completely forgive the affair. I then said that she could not in any way continue contact with him, no texts, no emails, no phone calls, and needed to fully remove any and all temptations from her workplace environment as well. She was VERY upset with my request, but reluctantly agreed... and now has done so 4 or 5 days after my asking her to do so. It has relieved a HUGE amount of stress from me, and has given her the clarity of thought to see what is important.
As others have said... God would NEVER send another person who is married to be with you while you are married. He wouldn't do so with a single man while you are married either. How could He break His own commands?
Please, keep your faith and seek counseling... you BOTH need it.
Have a blessed day,
-emptymailbag