Is this the first time you are asking him to end the A? And it has been this long? Just asking-not trying to give you a 2x4. Ok. Why do you suppose he is still married to you? He loves you and doesn't want to lose you- he didn't want to file for D right? SO... I think your best defense is to have very strong consequences in place.
You tell him he needs to end it. You want to rebuild your marriage and make it happier and stronger than it was. But you can't do that while he is having an affair with *&$# (now don't expect him to say "ok") "Are you willing to end your affair so we can rebuild our marriage?"
If he says "I don't know" or "No"- You say "I am no longer willing to be married to you while you are having an A." Then
You could do the classic move out of the house like they do in the movies- and not tell him where you are going, tell him not to call you but that you will contact him when you are ready. Be vague about why you are going and what you are going to do. But while you are away, yes this means he may be with OW but he has been "with" her several times since 1/8/09 right?.
You could ask HIM to move out and tell him not to try to contact you. If he doesn't leave then you get in your car and leave.
You could have a legal separation drawn up and ready then tell him you want him out of the house because you won't tolerate this A any longer.
You could file for D.
ANd yes I think it will help you to at least look into D (just to have the info and be less afraid- this is empowering as weird as it sounds- I just did it a month ago and should have done it long before!).
me,34 exH,34 S,16 months S:3/31/09-left for OW started DBing 10/09 d final: sometime 10/10 current: http://www.divorcebusting.com/forums/ubbthreads.php?ubb=showflat&Number=2022856&page=1 met in 2004
