If this is what you NEED then this is what it is. Unreasonable? Throw that out the window.
The OM/OW boundary IS an ultimatum, but not to punish the spouse, it is to protect you. You need to rebuild your trust in her and she needs to prove she is trustworthy. Trust was broken in the past time for her to pay the bill. Actions have consequences, for you and your willingness to try, this is her consequence.
The OM...this shitbird is going to try and keep in contact. To that end, you're likely going to jump at the wrong conclusions.
If you lay this boundary down on her and she agrees to it. Then you must know that this guy is still going to sniff around your X.
When that happens, as long as she is not the one seeking him out, then you should as part of the boundary tell her to let you know when he calls, drops by or emails her, because when you find out...and you will, if you are smart enough to VERIFY her actions, it will be bad for her if she didn't inform you. Because now it looks like she broke your boundary..and well..bye the fukc bye to her.
I simply told my wife, "If he is in your life in any capacity, I won't be."
Experience is a brutal teacher, but you learn. My God, do you learn. - C.S. Lewis
Life is usually all about how you handle Plan B. - Jack3Beans
Listen without defending; Speak without offending - FaithinAK
