Should my sons dad still pay towards upkeep for son whilst he is at local University and still living with me?

[Jaczacmum]

My Ex promised to keep paying maintenance for our son whilst he is at University. My son attends a local Uni and still lives with me.
Ex is now saying he is going to stop paying me when my son is 20 in a few month’s time, although he will still have over a year to go at Uni.
He doesn’t give my son any spending money or pay anything towards his Uni fees.
He states that because cost of living has gone up he needs to pay his girlfriend (who he lives with in her house) more money. So essentially taking the money from us to pay her, saying that I can afford to do without it.
He has never paid the amount of maintenance he should have for my son, paying only £100 per month for a few years, and then for the last 5, since meeting and moving in with his girlfriend has paid £160 per month.
I never took him to court over this as I didn’t want the hassle, but obviously he should have been paying far more.
Am I right to be annoyed that he is now saying he won’t pay anything towards our son’s upkeep?

Also wrt part time work, there is very little part time work that has set hours each week. Mostly it's whatever shifts the employer requires you to work including days, nights and weekends in combination. That's not compatible with any kind of timetable.

Most employers really aren't that rigid. DD works in a pub, she sets her availability on their work app and they allocate her shifts based on that, it changes from week to week. Most of her friends have similar jobs in pubs or restaurants and it works the same.

@HauntedBungalow

Right.

So you're not working one yourself?

Well, when I was a student, the phrase hadn't been invented, but even back in the 80s as a student I had different jobs on the go (babysitting, bar work, some what would now be called 'afterschool nanny' work) and yes, I used to be asked 'Can you work X date?' and I'd say yes or no.

Now of course it's much easier with WhatsApp.
Between them, my dc have worked
-retail (big, national company)
-retail (internet picking for a big supermarket)
-shop on University campus
-lifeguard in a Private club
-lifeguard in a council pool (2 different places, home and at University town)
-lifeguard hours at a school that hired out their pool
-in a noodle bar
-in pubs
-in nightclubs
-babysitting
-at a big leisure/tourist centre
-at a theatre
-in a chip shop
-in a coffee shop
-bar work at events (big cricket matches for example)
Probably some others I've forgotten.

All of the jobs meant they could turn down shifts when they needed to

I agree, @catin8oots . He clearly doesn’t give a shit about his son.🙁

We’re in the US so we’re expected to support our children through uni.
DD (19) is starting a full-time summer job the day after she gets home so she’ll save a good chunk of cash for her expenses over the summer. But we’ll still help her out when needed as we want her to have the best start in life that she can.

Exactly that. I would never put my son in so much debt. The point here which most people are missing, is that we both agreed to fund him through Uni, by him living at home. My ex had agreed to carry on paying me the small amount of maintenance to allow me to do this, but is now saying he is stopping it.
I will manage, of course, but just think he is being a total arse to do this.

Given that he didn’t even pay the correct CMS when your son was under 18, he's always been a total arse, hasn’t he.

At least you’re rid of him as a partner, it’s sad for your son though, stuck with a selfish father.