Here's the situation, help me out....

I was married for 10 years and had two children. Our last names remained the same after the divorce (my married last name). My now SO and I have discussed marriage however we both were recently divorced when we met and we're in no rush to hurry down the aisle just for a piece of paper. Anyway I am pregnant with our first child together and because we are not married, this baby will be born initially with my ex husband's last name because it is my last name. You just fill out the paperwork at the hospital and baby's name is whatever you decide (it will be his last name), no big deal. I have talked about the possibility of hyphenating the last name so that baby matches both me and my partner as well as our kids and he is deeply offended by this..... I don't associate my last name with my previous marriage at all, I just consider it mine and my children's last name (he abandoned them as soon as I filed for divorce). Am I wrong in wanting to hyphenate? Or is he being over dramatic?