OK assuming the OP is still reading.
OP your problem isn't that you can't go on holiday. Or even that you share care with an emotionally abusive arse. Your problem is you are stuck in a cycle of seeing yourself as a helpless victim, and make poor choices as a result. In no particular order, and by no means an exhaustive list:
Your choice of new partner is terrible. He's a financial leech, he doesn't share your financial priorities, and he is never going to make you happy, because you equate financial security with happiness (and there's nothing inherently wrong in doing that, so long as you tailor your life to that reality). So you need to kick him to the curb, or shift your priorities (I'd do the former rather than latter)
You prioritise a working life that gives you a freedom and time with your children that the vast majority of people don't enjoy. Which again is fine, but sits squarely at odds with you equating financial security with happiness. So you need to find a new job that might mean some compromises on time with your children, but will enable the things that you believe matter (holidays, own home)
You prioritise owning your own home over your mentally unwell child getting help. That is ridiculous, and means you allow your exH's abuse to impact on your child. Spend some money on getting him counselling.
You need to stop comparing your lifestyle to your exH's. Comparison is the thief of joy. The vast majority of divorced children live with significant differences in lifestyle across homes, get over it.
And, most of all, you need to get some counselling yourself on separating yourself from your exHs behaviour. He isn't going to change. The courts are unlikely to reverse the 50:50 arrangement. So you need to learn to detach and deal with it. Google grey rock technique. Read Lundy Bancroft. Do whatever it takes to take back control from him.
And most of all you need to boost your own self-esteem, and stop seeing parenting as being about material things. Being a good parent isn't about holidays, or owning a house. It's about providing an emotionally stable home where your children are supported and loved unconditionally. You did an amazing thing by leaving an abusive relationship. Build on that.