This is how I interpreted it all..
Kutner killed himself, he just wasn't happy, that's it. House wanted it to be more and wanted to figure it out, but he couldn't because there was nothing to figure out. He couldn't solve it, and just had to leave it at what it was, even though he hated that.
House did try and detox, but he was in such a fucked state of mind from the detox and his apparent psychosis that he did continue taking the pills. I think him and Cutty did actually hook up, but it was all the while House was on the pills. Since his hallucinations 'went away' because Amber went away, he started to actually hallucinate about his vicodin, which he thought was the lipstick. Once he realized that the lipstick was all a hallucination, it went back to what it actually was, the vicodin, and in return Amber came back.
Why Kutner was there, I don't know. Haha.
And in the end, House is actually insane. Or going insane. I was crushed that him and Cutty didn't end up together in the end, but I'm wondering if this will bring on another season or it's done?