On a more basic, general level, teenagers (and young adults) can come with all sorts of issues. Most teens are nowhere near fully mature and some might seem to emotionally regress to toddlerhood. Parental love and support being unconditional can be a very important bedrock for teens, even if (especially if?) they do not acknowledge it.
Your husband is absolutely right not to ever give up on his son. Think of the messages your husband’s actions send. Think of the messages that would be sent if your husband chose otherwise.
Best of luck navigating this relationship.