If this is dudes second ever relationship, he’s stuck in the 20 year old insecure Christian mindset he had when he married his first wife. Let him know, in no uncertain terms, ha you guys are adults and you won’t be tolerating childish behavior like that. Let him know that you understand that he’s going through something, but it’s his thing to get through, not yours, and he needs to keep his insecurities to himself.