Why are you subsidizing your roommate? You have a very weak case for abandonment; the only evidence of ownership is your getting the dog chipped...

How to handle a suit over tenant v tenant personal property?

This has nothing to do with animal law. Moving to lawsuits and disputes accordingly.

What steps can I take to get legal ownership on paper ?

It appears you have possession, meaning she would have to go to court to get the dog. "she is microchipped to me , registration is with me as...

There is nothing which indicates this has anything to do with animal law. I am moving it to criminal defense. The word you are trying for is...

If I bought a dog to try and save a relationship and it didn’t work out how could I get my dog back ?

The first and obvious step is to ask for the dog. If he is not being cared for, she may not want to keep him. If that fails, you would have to...

What legal trouble can I be in for taking my dog back from my ex?

You claim the dog was a gift, for which you apparently have zero documentation. He has documentation because " he bought him and always signed on...

Is this worth suing

Your fiance can discuss this with his doctor, and ascertain what, if any harm he suffered from this.

Can an emergency animal hospital and your personal veterinarian be held responsible for the death of your animals?

You state no facts on which a theory of liability could be based.

Am i even at fault?

The facts as given do not indicate any fault on your part. IF sued, retain counsel.

You might try an off-the-record/anonymous call to animal control, regarding nuisance animals trespassing on, and fouling, other people's yards, to...