Why do I feel so sad

So I literally don’t have any feelings left for my ex. I left him 4 years ago we had a very toxic relationship and let’s just say he couldn’t stop sleeping around with other girls. We started dating when I was 12! We broke up and got back together when I was 17 and broke up when I was 24. We were together over 7years. I found out he is expecting and I don’t know why but I got a sense of sadness. I have no idea why I have two children of my own and am married to a wonderful man. But why does it hurt? I know I loved him with all my heart but I knew he could never love me like I wanted him to. He always cheated on me he would be good when I would leave and would promise not to do it again but finally I stopped caring and i finally left. How come I feel this way why does it still hurt after 4years if not speaking and seeing each other can this still effect me. I feel so guilty to my husband I love him so much and he is so good to me. I just don’t know what is wrong with me 😞