Huge dog prescription bills... advice please?

Hello, this might be a strange question but should my ex contribute to my dog prescription/ vet bills?

My soon to be ex husband bought our family dog (black lab x) as a puppy from his friend 13 years ago, especially for my son and they've been best mates ever since. When the dog was 4 he became very ill and was diagnosed with addison's disease which he's lived well with ever since. Our basic insurance at the time only covered his initial vet bill and not his monthly prescription, which we used to get from the vet directly.
Over the years the tablets (thanks to the manufacturer's) have become crazy expensive until we arranged to have only the prescription from the vet and the tablets are now sourced from a pharmacy 30 miles away.
Now myself and my ex are no longer together and he's moved in with his gf and bought a new dog, he has no interest in our dog and never wants to see him even when he has the kids, but I have never stopped him seeing him.
The problem is is that the tablets are now costing me £215 every 3 months, with a £20 script charge from the vet AND a 6 monthly blood test and check up for £90 or they won't prescribe for him. Im a student and really am struggling to pay this bit if I text my ex to ask him if he'll help he just ignores me.
The only other alternative is changing his meds but this would be even more expensive to start with and the vet himself says he's thinks with the dogs age that he should stay on the tablets.

So my question is, do you think he should contribute to the vet bills as he knows how expensive they are? And if so.. would it be ridiculous to try and add it into the divorce or could I take him to small claims or would i be laughed out of the place?
Thanks