Custody

I have a bit of a complicated situation. My ex adopted a dog about 4 years ago. We started dating about a year and a half ago. About halfway through the relationship, we decided to part ways and he insisted that I keep the dog as he felt he would “hurt her” and he didn’t want her. I tried to support him and his mental health and insisted that she was his and he continued to try and push me to take the dog and I finally said yes. I brought her to the vet and found out she had gotten Lyme disease (he was not giving her tick or heart worm preventatives) so I treated that as well as her skin issues from allergies. This is all back about 6 months ago and now he is stating he wants the dog back and he was in a bad mental state. What can I do? Do I even have a case if he had the dog for 2 years before I even entered the picture?

Only a week ago, I verbally agreed to foster a 2 mo old puppy, that is special needs. She blind, and deaf. We have made great strides in her development. Just days after getting her, they contacted me to see if we were going to keep her or if they should put her up for adoption. At first I was very hesitant and unsure what I was going to do. So I said yes they could post her. The next day they had found a home for her with kids. And I decided it wasn't in the puppy's best interest, with her disabilities. Now they say no, I can't keep her. They want to spay her @ 2 months old, and 2 days later ship her off to Virginia. Again at the best interest of the puppy. I said no. Do I as a foster parent have the right to keep her?

So I'm going to buy a cat from a friend/roommate/coworker and I trust her and all, but people can turn around and stab your back in an instant. How do I make sure the cat is legally mine to make sure nothing bad happens a year down the line?