Feeling sad

So I found out my ex of 7 years is having a baby. I am also pregnant and for some reason I keep dreaming of him. It’s like I am jealous and I don’t know why. He was awful to me and it’s like what did this girl have that I didn’t. He always cheated on me and blamed me for everything. It’s like all these good things are happening to him and he made my life a living hell. I left him back in 2014 because he was cheating and I finally just stopped caring and moved on. I have a family and am married. I don’t understand why this hurts so much still to this day. His sisters keep trying to add me back on Facebook and I just honesty don’t want to see anything about them or there life. It was not a good 7 years and I just don’t get it. I wake up in the middle of the night and feel hurt and it’s been almost 4 years ago