@Iwasneveragoddess He has Aspergers. We never had him diagnosed formally as we felt it would have held him back but maybe we were wrong.
I think you were wrong. I'm a former special needs professional. If you had your son assessed he may have been eligible for extra time in his exams (not absolute, but possible.)
If he has an assessment at university- he needs to set this up with the student welfare team who can advise - he may be entitled to DSA ( disabled student allowances) which would pay for IT stuff like a computer and software and extra support if needed.
It all depends on the diagnosis and if there is also an element of dyslexia and ADHD. Bit puzzled how you know he has ASD without an assessment . There are also support groups for adults with Aspergers who can point him and you in the right direction.
I don't know why you held back on telling everyone there is only one child at home now- took me a while to work though all the DSS/DD1 blah blah but the gist of it is your son is at home and no other child.
You and your DH appear to have maxed yourselves out on a mortgage when you got together to extend your house.
You have come late in the day to the fact that kids at uni need parental support these days (yet you went through this with your daughter.)
There are issues around your current DH paying for your child (you even take this as far as him providing food for you both when he's not there to eat it which is simply bizarre!)
Whether he feels strongly about this or it's you projecting your own insecurities around it all, we don't know.