My SO cheated

We currently have a 11yr old and another on the way. About a month ago I caught him cheating. He has had this involment with this other woman for about 1 yr 1/2 on and off. She thought she was his only one. He denied I was pregnant to her. Also now I c why he was always bringing up the abortion and how I should have one. Now we have been seperated once I caught him and is being a total asshole towards me and my 11yr old. I miss him soo much but I bet it's just my hormones.