Most Helpful Guy
Well he's motivated enough too go the post secondary, so that's a start. Bring up the subject lightly. Ask him you'll support him all the way through, and hopefully he will feel the same way. Communication is key, one way or another, you're going too have this conversation with him. Has he told you what his main priority is if it isn't school? Ask him and go from there as a starter.
Most Helpful Girl
You cannot force him to become more motivated. There is no way to make him do that.
Odds are that he's going to get defensive or angry, no matter what. If you cannot tolerate the way he wants to live his life, then you should better break-up, instead of torturing yourself.