Husband hurting me during sex?

I have been married 16 years and found out a year ago that he cheated on me. We have been working it out but the sex has changed. My husband says that it's from his Diabetes and that's the reason he can't get a full erection. I have noticed that he can maintain an erection during foreplay but loses it before intercourse.This has left me feeling very undesirable and unsatisfied as he finishes quickly.The other night I walked in on him reading porn online and asked him to tell me about what he was reading hoping to get him interested. It started well and ended badly. He ended up anally penetrating me very forcefully. Enough to make me scream out and cry. He apologized but then penetrated my vagina and finished while I was still crying.This has left me confused and hurt.We have had anal sex before,but it was a slow process which left me time to adjust as it's not a normal occurrence in our love making.And the fact that he did not stop when he knew I was hurt. I can tell he feels guilty but he has been wanting me to make him feel better about it. I am the one who was left hurt and bleeding. Should I ignore this and act as if everything is ok? Why would he hurt me like this? What am I doing wrong?