While I am generally of the view that not all affairs are black and white, and that sometimes someone might leave their existing relationship to be with someone else, if you choose to have an affair, you are also choosing the responsibilities which go with that.
And those responsibilities include putting your children first, above the ex you decide to leave, and above the person you decide to leave them for.
If you’re unhappy you have the right to leave a relationship. But you do not have the right to trample over the innocent parties left behind. I.e. the children.
The children may be adults, but if they have chosen to not have anything to do with the woman their father left their mother for, and he is persisting on putting his happiness above theirs, that’s on him, not them.
Even if you’re genuinely unhappy in a relationship, you leave. If you bring someone else into the picture before that then you lose the right to claim unhappiness for your choices.
I don’t subscribe to the view that “once a cheat always a cheat,” but the truth is that if you do cheat, then you take on the responsibilities which go with that, and that includes losing your family if that’s the choices they’ve made.
You choose to leave your wife and children for another woman? Don’t be surprised when those children want nothing to do with that woman.
Nobody has the right to happiness at the expense of others.
If a man marries his mistress knowing his children will not accept her due to how they got together, that’s a clear indication he never loved them in the first place. If he did, he would give them time.
But this man hasn’t even bothered to try and divorce this woman he apparently was so unhappy with.
That tells you all you need to know about him.