How do I make my heart listen to my brain.

Lately I am having a very hard time letting go of my N and the awful things he did to me. I have read the books and have stayed active on the forum and understand that he is a worse case scenario narc. I know that this man is toxic and has made my life hell the past year and that he can and will never change.
The biggest problem I have is that I have always been so goodhearted and find myself being too forgiving at times and feeling sorry for people.
I know now more than ever I need to be strong and work on getting my life back, but I am so devastated that someone I loved so much could do such horrible things to me. I actually find myself feeling sorry for him, when I should be so angry at him! Who even knows if any of it is true, but I keep remembering the horrible abuse he told me he endured as a child and things that have happened in his life. I keep trying to remind myself its not my fault and he is responsible for his actions.
I am having this horrible ongoing feud between my heart and my brain. I am constantly on the verge of tears and feeling so depressed right now.
I am hoping that maybe this is the last step in letting go? My heart is so broken, maybe because I finally realize the man I loved doesnt exist at all if he could be so awful to me and that there is never a chance for us.