Ladies, how do you know when your family is complete?

My husband and I were set on 2 children. We got lucky and had a boy and a girl and we were thankful and said this is it. We even went as far as almost scheduling his vasectomy. Then he tells me while I’m 30+ weeks pregnant that he may want a 3rd down the line. That threw me in for a loop. I was set on just 2 until he said that. I started thinking and as my due date approached and I got uncomfortable I said nope we are sticking with just two. Well I had my daughter and it was a traumatic birth and I still said never again. She’s 4 weeks and now I can’t bare the thought of him getting a vasectomy and us never experiencing another pregnancy or birth or raising a child again. I can’t come to terms with her being my last. Why am I feeling this way?