England/Scotland.

• Relationship for a few years.
• I wanted a specific breed of dog (large breed) for many years prior.
• Partner was against it.
• I made it happen and got the dog, since I wanted that breed of dog.
• I bought the dog from gumtree. I seeked out the ad, contacted the seller, and bought the dog.
• Since we were in a relationship, I figured this was 'our' dog and they gave me half the money.
• They took care of the administrative tasks like insurance, microchip registration because they worked in vet industry. I figured this was convenient at the time.
• We didn't marry or cohabitate.
• We broke up when dog was 3.
• They lived around for corner briefly when we shared the dog.
• We verbally agreed to share the dog. Not much thought was put into it, no discussion was had about the future.
• They moved away home back to family for a year or so (12 hours away).
• They then got a new partner and moved away again. Still 10 hours+ drive, 500 miles away to the opposite side of the UK.
• Shared custody of the dog goes on for nearly two years, splitting up the year.
• Dog has been in my possession 8 of 9 months this year.
• I have dog registered to vet in my city.
• Ex has dog registered to them, in their city.
• Dog gets ill and I put a pause on the transfer until he's better.
• They demand that the transfer goes ahead.
• I question whether this arrangement is healthy for the dog, and wish to start a converation about it.
• They say arrangement is fine, and a disagreement ensues.
• Dog is nearly 6 years old now.
• They strongly disagree and want to make the dog travel thousands of miles per year to make the arrangement work. I disagree as I think shipping a dog so far and so frequent isn't good for the wellbeing of the dog.
• They offer to do all the driving, and I disagree because a 10+ drive multiple times a year doesn't seem good for the dog in addition to sharing two households.
• My priority is the wellbeing of the dog, not whose turn it is.
• I suggest dog has a stable life in one place with one owner, considering the dog's age.
• They threatens legal action and phone the police on me to open up a police file on me.
• They are adamant the dog is actually theirs, and not mine.
• I don't have the contact details of the seller.
• I have emails of purchase. Is this proof of purchase?
• Ex has dog's microchip registered to them. I'm not on microchip.
• I ask why I'm not on the dog's microchip, ex says the dog isn't mine.
• Dog insurance is in ex's name. I pay them direct debit.
• Ex stating that dog is theirs, and not mine.
• Ex is suggesting mediation, which I don't believe will be productive given how much we disagree.

What are my options right now? I don't want to be taken to court over this. Does my ex have strong grounds to take the dog away from me, or to have a court force the arrangement continue? I feel it's unfair that they can take control of documentation/admin like this, because on paper it may seem like the dog is solely theirs but I don't see that as the truth.

I don't know if this holds any weight here but can the comparison be made where a partner controls someone's finances, and thus controls the other person?

In my eyes, I see him as my dog because he was my idea and I pursued him, and got the dog. Ofcourse we shared the dog because we were in a relationship, and I shared the dog with my ex because I was trying to be kind and not hurt them. Now they are saying the dog is their dog and not mine. I believe my ex is willing to go all the way with this, and I am unsure how far this can go or what can happen here.