Just after some views on this please as not sure where to stand my ground and how to make this fair.
For context so no drip feed : Married, have one DS and one DSD. DSD is one year older than DS.
DSD came into my life 5 years ago, I dont have any involvement in raising her (DH has her weekends at his PIL house as we have a tiny house and no space apart from a sofa bed (my house when we met and we cant buy bigger as DH still paying for his exW house until DSD turns 18, live an 1.5 hours away so she gets bored at ours and can't see friends / do hobbies over the weekends if she was at ours so it just works best).
DSD has her heart set on going to uni - I fully support her in her decision as I want her to live her life and follow her dreams. DSD mum says she can't afford to assist with funding DSD at uni (she is low income through choice, works 16 hours a week to get full benefits (those who'll comment how do you know; she proudly told me and said she couldnt imagine having work full time like I do) as DH still pays for half the house and some of the bills under the divorce agreement until DSD turns 18). Our joint income whilst not huge means that me and my DH are likely to have to fund quite a lot of her uni costs. I dont begrudge her this as I love her and want her to succeed in life but here's the kicker....
My son also has his heart set on uni and is a smart kid and needs a degree for what he wants to do in a career. By myself and my DH funding my DSD through uni means there's no way we can afford for my son to go.
To not drip feed, my DS's dad died when he was very young so no financial input from that direction.
My DSD will go to uni, her heart is set and both her parents and I want her to go but where does this leave my DS? I cant save up enough to cover his costs from my income and it just seems so unfair his life choices will be limited by me funding a child who is not biologically mine. I want the best for them both.
How do I make this fair?