OP has never owned a home. Most likely for financial reasons, rather than the odd exceptional reason that people might be able conjour up, which is strict minority.
She's got a partner who doesn't like announcing her pregnancy, gravitating towards his daughter, probably feeling overly protective as the other parent is dead.
She earns less. Most likely a low earner, because of the house thing. Yeah, she could be on a million a year and him £1.2m. I mean, she's not, it's pretty obvious in context, but I guess some people just like to argue anything other than the most likely scenario.
He doesn't want to get married.
They've only been together 3yrs. His wife only died 3yrs prior.
And her support network is "My parents aren’t fit to help and I have no siblings".
Doing the pick me dance, and him clearly unhappy about it, but feeling dutiful/had the wrath of OP (who dismisses this widowed child's entry to adulthood, with her sole remaining parent, as "absurd"..."just a tennis trip") is not setting a great foundation, for someone already in a very insecure position.
He wakes up one morning, to "we can't go and see Sarah at uni, the baby is teething" and decides it's the straw that breaks the camels back, OP is homeless, low earning, no parents, no siblings, and raising baby. And not one thing OP can do about any of it. Something that might be a good idea to avoid, by handling the situation better from the outset.