14 yo gone crazy

I don't know what to do. my 14 yo brother in law lives with my husband and I. we have opened our home to him and welcomed him giving him everything he needs. today we found out he has been bullying a kid at school. my husband and I have both been bullied throughout school. we sat him down and told him he would be giving the boy a hand written apology and we would be taking him to deliver it. he told my husband to fu** off. I spoke up and said you will not live under this roof and bully people my husband tried to stop me but I wouldn't let him and said "no he just bullied you by telling you to fu** off" so he has now decided to move out of our house because he doesn't want to write the apology and apparently wants to keep bullying the kid. my husband is distraught I know he is going to go into a downward spiral of depression. what do I do? I suffer from bipolar disorder and bipolar depression. he is always there for me but sometime s I just want to be left alone. I told him I would be there for him and we would get through it but I don't know what else I can do.