Dorian is worried that who he is will negatively impact the Inquisitor. Either by giving the impression that he's the evil Magister taking advantage of the powerful figure he's seduced, or later on pinning a giant "please assassinate me" sign on his back should he travel back home with him.
Well, I kinda figure that that fell under, "which he explains quite well later on," ... not sure it needed explaining. 
More Tikaram praise: that last entrance through the eluvian when he mentions he heard about your 'light show'? And he says he knew you'd break his heart? You can hear the pain.
I don't remember the "light show" remark... but I took him with me all throughout the various things, so he would have seen it getting progressively worse, and did comment on it previously. But yeah... when he says, "Why didn't you tell me? We could have done... something... I don't know..." I was quite affected. I really liked what my Inquisitor said for the "I love you" dialogue option, but have tweaked it a bit in my head for my own guy.
It's interesting... in my head there is a real give and take as far as emotional support goes between Dorian and my Inquisitor and I really play that up in the fics I write. I like that that was expressed a bit during that scene. As you said, you can hear the pain, and can tell that Dorian is about to lose it. My Inquisitor is trying to keep it together for himself, for Dorian, and everyone else, so he offers reassurance for Dorian as well as himself, because if Dorian loses it than he would too.
Lol I thought it was the best dialogue in the whole damn DLC.
The next time I play I'll have to do reloads to see the other dialogue options, particularly the "I'm fine" one. He is displeased if you say something similar post-Adamant, so I'm curious to know what his reaction is here.
As an aside... I thought the British VA did well with all the screaming in agony in those scenes...