AITA for ended a relationship because of incompatibility?

I (23F) have made it very clear I have no interest in ever having children. It’s never been something I wanted and it’s something I make a point in bringing up in the talking stage of the potential relationships.

My now ex (25m) at first was on board with never having children and saying he was happy being the fun uncle. By this point, we’d been together a year. Well, recently his sister (30) gave birth to her first daughter after having three boys. My ex “Jack” was instantly obsessed with his newborn niece. He’s been going over daily to help his sister and watch his nephews while his BIL returned to work.

Well, after his first niece was born, he’s been talking about how much he’d really enjoy having a little girl of his own and how much he’d enjoy being a dad. I reminded him that I really did not want children but if he did, I understood and wouldn’t stand in his way of finding a woman he could have a family with. He said he knew but maybe I would change my mind after spending time with the new baby. This isn’t something I’ve ever done as I believe new parents should have the right to decide when/who was around their newborn and his sister had always respected I didn’t like children and had never asked me to babysit her newborn. I did help in other ways like cleaning the house, cooking meals, laundry etc. just not babysitting.

I very reluctantly agreed and his sister even asked me several times if I was sure I was comfortable. My boyfriend insisted everything would be fine so I told her I’d be ok. Well, I wasn’t. I couldn’t take the crying. It was like nails on a chalkboard for me. I barely lasted 10 minutes before I handed the baby to her mother and apologized before I left.

My boyfriend was very upset saying I barely tried to take care of the baby. I reminded him that I didn’t like kids and this was one of the reasons I didn’t want them. His sister later texted me saying she was sorry she didn’t insist on her brother leaving me out of this and I told her it wasn’t her fault. Finally I told my boyfriend we needed to have a serious conversation about if we were even compatible anymore. He agreed to the conversation.

I asked him if he wanted kids now and he said yes right away saying he wanted a little girl of his own and how great it would be if we were to start a family. I was a little upset when I heard this but I remained calm. I told him that I understood he wanted a family but I still very much did not. I told him that I loved him and thanked him for a great year. He asked what I was talking about and I told him I was breaking up with him because he wanted kids and I didn’t. That there was no point in us staying together anymore due to the fact of him wanting kids and I not wanting them.

Thankfully we do not live together so there’s no need to find new accommodations and I’ve returned his key. He’s been texting constantly begging for another chance and saying he’d rather have me than have kids. I don’t want to run the risk of either 1) him tampering with my birth control or 2) resenting me for him not having kids.

I feel like I’m an ass because until this, we had a great relationship and were overall pretty happy. Our friends and families were divided saying that since he changed his mind, maybe I will too. I don’t believe I will as I’ve never wanted kids since I was a child.

So AITA?