<human>: Can you condense the text into three sentences or less?

My mom is 70 years old.  She's been married to a man for 20 years (not my dad).  He is ill and may need heart surgery.  
She has cheated on him before, travelling and visiting with other men, carrying on relationships behind his back.  I don't know how long it has been going on, but it has been going on for years.
I don't approve because she is dishonest with her husband and doesn't love him, I believe she's just using him for money.
Yesterday she says that she has seen a lawyer and has begun to look into how she could end the marriage.  At first I thought it was good, because she was finally going to be honest with him and end it so they could both move on.  But then she says she hasn't told her husband yet because "it could kill him" due to his delicate health.  So it's okay for her to cheat on him and spend his money, have relationships behind his back and play him for the fool, but lying to him could kill him.  I asked her what if he found out through other means; she is convinced he won't.  I think he's not a fool, and that he knows that she's been cheating on him and just tolerates it.
Anyway, she's visiting my family soon and she's bringing her new boyfriend with her.  This is the second time this has happened.  The first time (different man) we shunned him.  The situation was awkward and ugly.  My wife and I have three children, the oldest of which is 11.  She is certainly savvy enough to know what is going on, that she is there with a "friend" and not "grandpa".  
My inclination is to not see her with this man, not have her visit our new baby.  
Advice?
<bot>: Older mother with sick husband is cheating on him, wants to bring boyfriend to visit, we don't want them to be around us or our kids.