My brother's wife's sister has a unique problem. After 20 some odd years of marriage, her DH comes home on day, tells her he no longer loves her, announces he has a girlfriend and leaves to go live with his mother. The a$$hole has a good job, makes good money and does meet his obligations. However, the kids (twin girls aged 16 and a boy, 15) have serious emotional issues over the change in dynamics, etc....

She wants a divorce and be able to move on and put this behind her. She is approaching the big 5-0 but is a very nice and giving person, and could make someone happy. But she is stuck for now, and her stbx (?) is paying expenses as if they were still married, but I guarantee that as soon as the youngest is 18, that's over. She has a decent job, but cannot survive on her salary alone. So she has to allow status quo for now.
She recently told me that he wants to come back home but will not promise to stop seeing the other woman. Sounds like serious mindgames. Without making judgements (and I know there are some out there who are capable), what kind of advice would be the most help?