What's fair to the ex-wife?

[DarrellRiversIsMyHero]

Me and DP have a gorgeous 3 year old together. He has two children (19 and 17) with his ex-wife.
When he and his ex-wife split 7/8ish years ago, they made no changes to their finances, and that has never changed. He continues to pay her mortgage and bills in full and is named on all of them. We (him, me, our child) live in my house, which I bought before we got together. I continue to pay all the mortgage and bills for us and he pays for his ex-wife.
Now his youngest child is nearly 18 and he is attempting to negotiate a finance split with his ex-wife. I'm trying to keep as much out of it as I can - it's non of my business - but I have no idea how a financial settlement works when so much time has passed since the split. Will he have to continue to pay her to live in their old home? She cannot afford it on her own (it's a much bigger property than the one he lives in with me). And for how long? Will the pension split be based on what they each had 7 years ago, or where they are now?
We are extremely keen to be fair to the ex-wife, it's just very hard to know what "fair" looks like. Right now, I have to work full time to keep our family on the road and I paid for my own mat leave out of my own savings.

Any of your own experiences with finance settlements, and how you felt about them would be very welcome

(edited - spell check)

She still has a career, no housing costs, no utility bills and the kids are both nearly 18. She’s had years to start paying her own way. Having been married and had children doesn’t entitle anyone to indefinite support. And they’re her children too.

I don’t judge her, she’s taking what she can get, not very dignified but fair enough. He’s the one taking the absolute piss by using OP to fund his generosity.

What is the equity in the house and what mortgage potential does she have - and what can she buy with 50% of the equity? Is it reasonable to expect her to rehouse with this sum?

She might have an entitlement to more based on the years of being maintained by her ex (or you) but hopefully nobody is going to want to drag this through the court for a year or two.

Thanks, BruceandNosh. I've never seen it that I pay for him. We're a family, we live together and I'm happy to play my part in that. As for savings, I have no clue about his ex-wife's financial situation, but I'm a good earner, I'm making sure that we're secure. It sort of feels reasonably balanced as there are three adults, two of which are good earners and one of which is not. So between us it all worked out, especially when his two eldest were younger. If I was to look at it from a very transactional, financial, pragmatic point of view, yes, I am (financially) much worse off in the arrangement and his ex-wife is a beneficiary, but the security and happiness of all the children is a very big factor

Thanks, Mumof3 - I think that's a good point. Rather than looking at it from a court point of view, work out what she needs to buy herself a house and run it independently. I originally started this thread to understand the viewpoint of people who have been through it from a different angle - it's never been about getting as much as I can out the deal. I've been happy with the arrangement til now, it may be unconventional, but it's worked for us

Oooh, no! That's absolutely not the case. No judgement either way but that's not how it happened and no-one thinks that.