Men’s Morals

I think if you can maintain your boundaries, you can still interact with him if you wish, with the crystal clear message that his attitude towards his wife has made clear to you that he’s not a man you’d be with in a million years.

Hmmmm I’m not sure your morals are squeaky clean here either OP. Being the “work wife” tends to lead to this kind of thing…

“Would continuing on a flirty friendship continue to give him a green light and feed his ego?”

He sounds highly unattractive and you sound desperate for the attention.

Don't see the point of "continuing a flirty friendship" unless it's what you want. You can't really continue something like that without one thing turning into another and in this scenario ultimately ending in cheating. Once a cheat, always a cheat. Not going to be any different with you. It's all until the next best thing comes along.

have always kept him in check with a very firm boundary

I have told him we may, or we may not,

So you didnt "kept him in check with a very firm boundary " you didnt cut him dead, you enabled it?

If my friend approached me saying we may have a future he'd be told dead centre, no bones. No niceties

You didnt do that.

Tell him to fuck off. Tell his wife shes married to a sleaze and suggest she gets her ducks in a row and divorces his ass and walk away.

wow like you’d want the sleaze at anyway if that’s how he treats people!

Tell his wife. If he doesn't leave for you, it'll be some other poor woman he wants to monkey branch to. The woman he's married to deserves better... Certainly not a man who is just looking for the opportunity to leave.

If you really want to be all chaotic good about it, lead him on, tell him you'll be with him, tell him to give his wife everything in the divorce to make it easier with absolutely massive child /spousal maintenance and he doesn't need anything anyway as you'll cover it for both of you as you're so in love ... Then ghost him when it's all done lol.

Any man who establishes a relationship (whether physical or emotional) with another person will do exactly the same to that very individual. Steer clear and make sure your boundaries are tight. Why would you even entertain him by saying you might consider it. His partner is wonderful and they have kids together. The lack of loyalty and respect he exudes would make my vagina clamp shut with a snap.

No, cut him off. He has been inappropriate and showed you his true colours. He should not have said such things at all, dreadful. It's perfectly OK to cool off from him. He is not a good guy.

I disagree that all men are like that though, they are not. Find a good one and keep those firm boundaries.