So, still the "You have to break off all contact with exes you are still on good terms with if you want to date" line.

If the new partner KNOWS and is okay with it, then it is not a problem. I have been in communication with all but one of my husband's three serious exes...and the other one is no longer in our life. I've gone to girls time with one of them. I've let him have lunch with the other. She's married and has a kid. I trust him.

There are no rules. Especially ones you shouldn't even have to state.

There are your rules as a couple.

Just because somebody is a compatible gender does not mean you are sexually attracted to them. Period.

This is still flirting with toxic monogamy.

Having a private conversation with a friend of a compatible gender is not cheating.

Bear in mind that for some of us these rules would mean "No talking to anyone without your spouse present unless it's related to work. Anyone."

One person cannot provide all of your emotional needs.

Now, I do agree that if your friend is constantly complaining to you about their spouse/partner, there's a problem and no, you absolutely should not be their unpaid marriage therapist!