Am I the asshole for lieing to my Ex to keep our dog?

Ok so I asked a little while ago if I was the asshole for how I ended up with my ex’s dog. To sum it up real quick:

My ex and I were together for about 2 and a half years and we shared a cat and a dog. When we broke up, he took her and I kept the cat. Months went by, and then one day, I got a call from animal control while at work. They found her wandering without a collar. Since her microchip was still under my name, they called me. I attempted to get a hold of my ex but couldnt. At the time I thought I was blocked, I've since found out he changed his number. I called his Mom and explained to her and asked for somewhere to send the dog. I waited and got no response. So I asked them to bring her to me.

I took her in, got her settled, and have been taking care of her. I have two other dogs already, and she clicked with them. She seems happy, comfortable, and honestly, like she belongs here.

Here’s where the lie comes in after almost three weeks of no contact, my ex suddenly reached out asking about her. I told him I hadn’t seen her, and that I didn’t know where she was. I lied. I know. But I just didn’t trust that she’d be safe with him again. I don’t know if she escaped or if he let her go—either way, she ended up alone and collarless, and I feel like that says enough. Taking that long to reach out made me just not want to return her. Selfish, I know

Now I’m struggling with guilt. I don’t want to be the villain. I love her, and I feel like I’m giving her a better life. But I still wonder if lying to him makes me the asshole, even if my heart was in the right place.

So Reddit—AITA for lying to my ex so I could keep our dog?