1. Open up to him. Broach the topic when you're alone and calm, but don't nag. "Nothing dampens a person's will to change faster than belittlement," says James Claiborn, PhD, coauthor of The Habit Change Workbook. Instead, be direct. "Let him know how the habit affects you and why you think it's important for him to break it."
2. Have some backup. "If your guy denies having a problem, keep a mental log of how often he indulges," says Claiborn. "Sometimes confronting a person with firm numbers helps them face reality." But if he won't change, you need to think about whether this is non-negotiable for you.
3. Offer help. Say you get lucky and your man says he’ll quit—smoking, gambling, whatever. Next, ask if there's anything you can do; don't just assume that because you inspired the change, you'll be part of his recovery. "It's important that you're there for him—but his way," says Claiborn.