Before you say yes, get him angry. See him scared, see him wanting, see him sick. Stress changes a person. Find out if he drinks and if he does get him drunk– you'll learn more about his sober thoughts. Discover his addictions. See if he puts you in front of them. You can't change people. If they are made one day, it doesn't just wear off. If you hate how he acts when he's out of it now, you're going to hate it much worse eight years down the road. You might love him to bits but it doesn't change that some people just don't fit.
