So, John's ex I will for simplicity call Jane. I'll just have to tell this as a story to understand the cheeky fuckery of John.
Young Jane inherits a home, needs a lot of work. Jane gets small mortgage to cover works. She has a job that is relatively low pay, requires shiftwork. Meets John, who has 'big career'. John moves into her house. Jane gets pregnant, has their kids. John doesn't contribute to any house stuff even during maternity leave, she covers it from her maternity pay and savings. So he has zero claim.
At some point John starts cheating with a married woman, and she gets pregnant but isn't sure if baby is John's or her DHs. John does paternity test, not John's and she breaks off affair. Jane finds something related to the test while on maternity leave with youngest, confronts, splits up.
John moves into rental with ridiculously kind hearted family friend who gives him rental at reduced price (basically as low as they could afford to live on considering its their retirement) so he 'has a place to see his kids' and money for lawyers and court because 'that bitch has bled him dry and won't let him see the kids'. In actual fact he hides his earnings, refuses to see the kids, lives a life of luxury. Jane has to go back to work so she doesn't need to pay back her maternity pay but due to shifts no childcare available and John says her problem and tells everyone else he's busy (on holiday, buying new cars etc). We, along with other friends, step in and watch kids until she can move to a new role on shifts she can get childcare.
He keeps posting his victim-woes, cost of living goes up, family friend can't afford the low rent anymore, sees stuff about him struggling to pay what little they're charging him. They go to talk to him and say they need to charge market rent. He kicks off, slips up in his rant and reveals he cheated, they also see lack of kids stuff, fancy new car on drive etc. They end up going for section 21.
It's caused lots of further issues within his family - his mum has basically lost her best friend for lying to her. John waited until the bitter end to beg DH to take him in, so he's had to move his stuff to his parents house and is staying in a hotel here when he has to work. He does have a new (young) girlfriend, but cost of housing high here so she's still living with her parents that hate his guts.