Drink at night. Then send a message to your ex. How should I reply and forgive him when I wake up the next day?

If you explain, you can say sorry, you drank too much last night, and then things got out of hand. You may have sent something that was, um, not very good or reassuring, so you didn't mind, and then you were sorry, and then you didn't mean to disturb you, and then you may have drunk too much yesterday and lost control, so I apologize to you. Don't think too much. The past is the past.