L.N.
actually i know how your husband feels, but i also know you did the best you could. my advice to you is never deny that you didn't stand by him when it came to your mom. denying it, even once, will make things worse.
i doubt he will get over it. it is an emotional scaring to him, and you need to accept that.
that said, if you're ever in a situation like that with your mom again, make sure your hubby is present, when you put her in her place.
let me get this off my chest too: my husband's mom (calling her mother in law makes it too close to me and i don't want that), has been nothing but a total b.... to me and then my kids when they came along. my husband never stepped in, but made excuses for her, saying she's aloof. I waited quite a long time (never for years) to make her realize what she was doing and apologize. once my kids came along, and she had the same attitude towards them, it became clear to me that she needs to know this is wrong, that i know she's being hurtful, and i spoke. once i spoke, all hell broke lose. she played dumb to the whole situation, and even called my medical problems (read medical, not emotional) for my outburst. but when i did finally speak up, all ties were cut. my husband doesn't see her. he calls his dad once a week, if she happens to answer the call they'll talk for a few minutes exchanging pleasantries, and that's that. she doesn't ask about me or the kids nor does he offer. he did stand by me silently as in he never insisted on visiting them. but, to me, that was not enough. had he spoken up when things were happening i wouldn't feel betrayed as i do now, years later.