Don't. He isn't all that special, Mocha.
When you're on the same path with someone and you're headed to the same place, you both know it. If you feel the need to question them, you probably aren't. He already told you he hadn't "thought about things" and that tells you all you need to know in a nutshell.
Men that aren't in relationships for the long haul HATE this line of questioning. They'll stick around while it's easy breezy but when you start asking questions and making demands, they scoot. This isn't necessarily a loss although you may feel so at the time. If he is good for sowing oats and such, sow your oats but keep your eye out for the real deal. He's not going to be the one.