Why is grief so weird

So about two years ago I divorced my high school sweetheart. I was with him for 7 years and lived with him and his parents and we also had a daughter together. The divorce went pretty smooth my emotions were in check I knew it’s what I wanted. He was mean, controlling and all over the place and he’s that way with his fiancé now. Well now I am with someone else and we now have a daughter together we got together shortly after. For almost two years now I have never looked back I was happy with my life. For some odd reason though i cried randomly about it. Sometimes when his mom talks to me I do miss that conversation and its tough. His mom also sends me pics of his sisters new baby and that brought some emotion out of me and I couldn’t figure out exactly why. I’ve been fine? Why all these new emotions later down the road? It sucks..