What's a Stepmother to Do?

Okay, I have a sleeping teen. I know that is not all that unusual, but c'mon, it is 1:20 pm.
My 'son (He's my stepson, but I will call him 'son for short; he DOES have a mother) came to live with us suddenly when he was 12-going-on-13, in the month of March, as he was in sixth grade (painful enough in itself). He went through a lot of emotional pain, got himself sick with it and missed a lot of school the first year with us. After that, I think he decided he could not afford to screw up school on account of someone else's craziness, so he focused on saving the justice system that caused all this. He went through the normal gawkiness, schoolkid cruelty and friend-making stuff for that age, and by the time he was in High School, he was pretty much focused on being an honor student and a senator or something. This all went along swimmingly for a few years, gaining trophies and certificates and getting to school early every day, ignoring girls and playing strategy games on the computer. Since he has a "curse" of winning most games he plays, I think things were going fine, until June of this year, when he attended a convention put on by the American Legion. There, he had to wheel and deal for Mayoral positions and offices and such. This wheeling and dealing did not go well; he learned he did not like it at all. All political aspirations went down the tubes.
Now, let me tell you, we did not steer him towards "politics." We had to tell him early on, not to tell people he wanted to be a "politician," but to say he wanted to work for Government. He dressed up in a suit and tie for church, while we were dressed quite casually. He is "clock" person, always wanting to know what time things are and he is rarely late, if ever.
Ever since he turned 18 this year, he has changed his persona probably about 3 times. After this experience with the Boy's State, he started working out, slimmed down, got a cell phone and started becoming interested in dating, really interested. He was interested in his TAN. Yikes! Then, he went out to Kansas to visit his mother, brother and sister for the first time since she took off with his siblings in 2001. He could show himself to be an honor student with a healthy bod and a cell phone. He was OKAY. Then he got back home and had no idea who he was anymore.
At this point, he stays up all night online with people we've never met (who knows if he has either?) and sleeps way, way, way too much. He decided he is not so smart and even wanted to just quietly go to a Kansas community college. (He's moved on from this idea, thankfully) He does not come downstairs much and hardly eats. Descriptions like this are usually ones that go with Drug Use, but that is not it; I think it's Depression. My sister, who's worked with youth for years says it is normal. Normal is one thing, but how about healthy? What do I do for him? So far, I feel what I can do is to continue to invade his space (lightly, with respect), pray for him, involve him as much as possible, keep checking on him and asking him how he is, but I feel like I need to do more.