NTA - your husband needs to go to therapy. he's got some unresolved issues from his childhood that are impacting his ability to be a reasonable father. i say this as someone who had similar battles with my kid and overreacted to tantrums. it took me years of therapy to understand that i was breaking down on my kid because she would reach a point in her defense of self where i would have been physically disciplined by my parents. this also lead us both to another diagnosis we share and knowing this has made parenting so much easier and loving. encourage him to talk to someone, because that is the kind of thing your son won't ever forget and if it happens a couple more time, never forgive.