Harry should state that he will never take a drink of alcohol again, because he sees what it does to him, especially his judgement. He is "allergic", better word "sensitive" to alcohol and it makes him behave this way, whatever you call "this way". If he doesn't do anything else for his country, the monarchy, and himself, it would be a contribution for him to swear off alcohol. He doesn't need it to lead an interesting life. He already has an interesting life, and it could be very much more interesting if he got straight on this and reexamined his values.
I can barely understand the comments on how Harry might have done this to make sure the girls at home knew he was not ready for marriage. If marriage is such a desperate situation for Harry--to be feared--so badly, maybe he should start thinking about finding a worthy life partner, and being alcohol free would help him find such a partner.
He probably should marry fairly soon, and if the only way to do it is to resign the army and work "at home" for his family, that would be a positive step. But who is helping Harry think straight? He sure needs a mentor. A guide. Maybe even a clergyman.