...as impossible as it may seem to do but it can be done. I've lived past what you are asking, and you can cry, beg and plead but they are set in their mind that they are doing no wrong, so they in fact believe it , just remember for every action there is a reaction, I advise you to pick yourself up shake it off and take care of you so you can take care of the ones depending on you, It seems they turn to dogs that want to raom and when they get tired want to come back home, because they know the way back don't let him back in, however only you know what you feel for him and if you are willing to let go completely, you can't make a person love you or care for you if they don't want to. Love you because you are worth it.

My first coping mechanism is to ignore it.
When I can no longer ignore it, or rationalize it away, I criticize the other person's behavior and list everyone who is being hurt by it. I have yet to hear, "By golly, you're right. Thanks for pointing that out to me."
Okay, if my sweetheart won't listen, I'll confront her boyfriend. It didn't take much to provoke him into throwing the first punch so I felt justified in punishing him. On the day of my acquittal the judge said, "You got away with it this time, Mr. D-, but you don't want to be in front of me again!"
The only thing that worked, for me, was, as V.B. pointed out, was patience and forgiveness, but that was impossible as long as I focussed on 'the wrong thing that she did' which needed to be forgiven.
I have no idea how it came to me, the thought that her behavior was caused by an undiagnosed brain tumor. Preposterous, aint it? People don't choose to have a brain tumor. But when I allowed myself to believe that, I experienced true compassion and a genuine feeling of peace.
Looking back on it I see that forgiveness was an unconscious act, it is a fruit of true love. When I am 'trying' to forgive... it goes like this; you've really hurt me, okay, I forgive, now will you come back and love me? The harder something is for me, the bigger reward I look for.
Suz, I am really glad that your question was at the head of the list today. I recently heard that my sweetheart is engaged. I've been trying real hard to pray for her happiness. I had forgotten that she has a brain tumor (take my advice,...I'm not using it). Thanks for the reminder. You are not alone in the struggle.

I'm reading this really good book by Gary Chapman called "Love as a Way of Life." I just finished the chapters about Patience and Forgiveness -- I wish I could send you some because it sounds like you need a boatful for this person right now.

I commend you for understanding. Like you say, this is not normal for this person. At the same time he needs to know that he may have crossed a line with his reckless behavior.

I think what you have to decide is how far this dalliance can go before you have to walk away. If you can't forgive when he's ready to come back you'll have to release this person. We all have a responsibility to each other. As you're considerate of his needs right now, he needs to do the same for you.

I think you'll know what the right thing to do is if he does indeed wipe the mid life mist from his eyes and wake up.