I should have clarified....don't tell him he has two weeks, just expect for him to cut it off in that time frame or sooner. I've learned with my H that the contact would end, and not because of me, because of one of them and then it would be radio silence for a week or two or three and then start back up. And it went on like that since late January.
But my point is this I guess....give him the ultimatum if you are comfortable with the possible outcome that he says no. I don't think he will. But give him a couple of weeks, and only you know you are doing this, and let him end it. These OPs are very much like a drug and it's hard to quit them. After tht time frame or even a week, if you still suspect he's in contact with her, do what you have to do.
With my H and I he's decided in his head, not mine, that he didn't cheat on me because we were/are separated. I have no doubt in my mind I could have served him papers in January and he would have signed them because he was so sure then he wanted out and wanted a new life without me. Now I know from a little birdie, he's glad it didn't come to that.
Setting boundaries, giving ultimatums, there's timing involved in all of this. And you have to be ready for the worst case scenario.
What will be the outcome if he doesn't agree or goes beyond the boundary?
