Ex partner and dog - Help needed please :(

[Doghouse1g1]

Hi all, I split with my ex partner 7 months ago and have shared custody of our one dog, she is 6 years old. I have her majority of the week and he maybe takes her a night or two every week.
My issue is 5+ times now she has been returned to me with an upset stomach, vomiting etc. She also went missing in his care for 3 hours at the beginning of our separation. I have also been told by mutual friends he leaves her alone for long periods when he goes out etc.
There are no set days he takes her, he works away a fair bit so can be gone up to 2 weeks at a time. Its of no concern to me what he does with his free time but he tends to message me last minute when he can/cant take her and I have to arrange alternative care or ask a family member to take her.
He is not responsible enough to care for her alone, when we lived together I fed/walked her 99% of the time and I worry sick everytime he takes her :(
She is microchipped to me but he has paid her care the last 5 years (split food and insurance etc)
Legally can I stop him seeing her? I feel guilty (not a bad breakup) but I am concerned something will happen to her in his care. We have no children so she is like a child to me...

There isn't a simple answer because only a court (and really, that's a ridiculous expense) can decide, but generally ownership is determined by things like who paid the purchase of the dog, whose name is the microchip in and who insures the dog. Frankly if you feel this trongly about it then to refuse to let him take the dog and it's up to him to take it to court. I doubt he will.

I would just text & say he can’t take her & she’s chipped to you. No way I’d be letting my dog go to anyone that didn’t properly care for her.

Shes chipped to you, she's your dog

is it your name on the insurance and at the vet?

if so unless he’s got a receipt or something from getting her in the first place in just his name then he’d have pretty much no case if he did go to court.

Maybe of use if live in England/Wales.
https://doglaw.co.uk/civil/ownership-custody-disputes/

Microchip alone actually isn't proof of ownership as it's the registered keeper, the person the dog normally lives with who may not necessarily also be the owner, bit like car's.

If he's away most of the month and is going out for long periods while has the dog he may even be glad to drop the obligation and not object as much as expect.

Microchips aren't proof of ownership unfortunately - whose name is the insurance in? Who is she registered with at the vets?

All those combined could paint a better picture of her being your dog.

So no kids involved?
The dog is with you most of the time? Microchip in your name?

If the vet is registered in your name too I would just send him a message saying youre no longer letting him babysit your dog and block him on everything.

Why don't you just talk to him. Say something like "i notice you're travelling or going away a fair bit. Do you want to review dog share arrangements? I'd be happy to increase my time with dog but it's a lot easier for me if I have a fixed schedule"