How to handle cheating

Recently I found out that my fiancé cheated on me back in October with his of 4 years. I assumed and had a feeling all these months that he was still messing with her and I was right about every single thing. I never been cheated on in a relationship and I dont think Im taking it the way Im supposed to. Its like my body rejecting and denying it. Ive been laughing at the situation , more hyper than usual , Ive said I forgive him and want to move past it , Ive barely cried even though it hurts so so so much , and one main thing is hes making it seem like he feels horrible about the situation but for some reason Im stuck on making HIM feel better and trying to comfort him as if Im the one that cheated. I cant even focus on my feelings and I dont know why my body heart and mind are doing this. I just want someone to help me understand myself