I am a gay man who is in a relationship with another man who was married for many years and then came out of the closet. He has maintained a very good relationship with his children and ex-wife -- perhaps too good, in the latter case. His ex-wife refuses to move on and date new men, and still clings to her ex-husband, calling on him at all hours, expecting him to help her out, and be her best friend no matter what. Out of guilt he runs when she calls because she was devastated when he ended the marriage. I know he has no real feelings for her anymore, but it's clear that she just can't let go. And she's always hugging and kissing him -- he claims it's just affection and out of habit-- and sometimes he even comes back from doing a chore for her with her lipstick on his collar from a "thank you" hug. Ron in Albany.
Well, at least her lipstick isn't in other places -- you hope! I understand that your lover is feeling guilt and yes it's good that he and his ex-wife get along and he remains close to his children, but a line has to be drawn and you've got to establish that line if he won't. You may eventually have to sit down with the ex-wife and in a compassionate way explain how you feel, that you're trying to build a life with your man and she needs to move on. (Know any nice straight single guys you can introduce her to?)
You also have to make sure that these "chores" he's doing for his wife aren't sexual in nature. He may still be a bit uncomfortable being in a relationship with a man after so many years with a woman and feel some kind of "macho" need to engage in hetero intercourse -- for all the wrong reasons. Cheating is cheating, no matter what. And you need to know if he's still conflicted.
Even if that's not the case, the situation here needs to be "straightened" out before it gets worse. The more the ex-wife believes she can take advantage of your lover, the more she will. Ultimately, it wouldn't make a difference if your lover had moved on with a man or another woman, he's with somebody else now and the ex has to accept it. He shouldn't leave it to you to handle the situation.
Sit down with your lover and tell him how you feel. Remind him that in this case guilt is a useless and even harmful emotion -- harmful to the relationship you are both trying to build together. Hopefully, once he realizes that he might be jeopardizing his future with you by overly coddling his ex-wife, it will be easier to him to say "no" to her. He also needs to understand that the more he coddles her, the less likely it will be for her to look for -- and move on with -- somebody new, which isn't good for her. The hugs and kisses she gives him may be merely "affectionate" and meaningless to him, but they are in no way meaningless to her.