Be His Accountability Partner

Once the bad habit has been brought to light, help him be more accountable. Not in a way that you are constantly bringing it up but in gentle reminders.

You should both decide on a reminder that won't be offensive. Using the dirty clothes as an example, instead of shouting, "There you go again, leaving your mess all over for me to clean up!" turn it into something more playful.

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Remember that bad habits don't change overnight. Expect him to slip up and at times even resist. How you react will determine how the situation plays out.

When it comes right down to it, no one can really break someone else's bad habits. If you try to exert your will over another person's life, it usually ends up backfiring. They have to be willing to make the effort, but you can be their biggest cheerleader.