I don't know and can't say for sure because I'm not a trained therapist/psychologist/psychiatrist but it seems to be that your husband is the one that needs mental help.

Yes, it seems that you did have a minor little thing with some other guy based on what you wrote and without knowing the full story I can't say if you were justified in what you did or not. But, the punishment doesn't seem to fit the crime.

The past is the past and if he can't accept that then you need to move on. He shouldn't keep using it to beat you over the head.

This sounds so much like other people I've known and I'm going to give you the same advice I gave them, "Freedom is spelt D-I-V-O-R-C-E!"