This is adorable. 
Thank you. I donate every 'like' to Lavellan's "FIND SOLAS" fund. Your souls now fuel her reunion, BWAHAHAHA.
On topic: Oooh yes. Yes. These conversations are goooooooooooooooooood!
----> So in regards to discussion on the orb earlier and it being of Fen'Harel/Solas -- there was some data mined info that referred to the orb as that of Mythal. Could've been just an inside reference for simplicity, could've just been an asset name... OR it could have been something Mythal had locked away at one point. Who knows? :>
---> Solas absolutely has trust issues! I think there's more than enough dialogue to support this and that it is canon. I think it Fen'HALARIOUS that when he chickens out of telling her all, the first thing he thinks to say is the vallaslin bit. Because it is literally staring him in the face. Smooth move, Dread. But oh, how smooth he really was, because you're right: it is something both distracting and monumentally characteristic of him to want to educate you. He is a scholar. He is a fighter. He is a god -- but undoubtedly raised to that status much like how the Inquisitor is raised to the title of Herald. Not of his own free will. With this in mind, I support that he is vulnerable and wounded and accustomed to being shut out by those he tries to help (ie: Dalish clans who call him a madman) -- and thusly, he would indeed be fearful of telling an elfquizzy about the slave marks. She might shut him out too -- his friend, his vhenan. But when you romance him, that love establishes such a connection that he feels he can tell you anything. Anything. The fact he nearly spills his own truth reveals how strongly the romance affects him. So sad.
As was mentioned earlier, he does say "you saw more than most".
---> Also, the magic he uses to renew Lavellan's face -- it's a very similar colour as the old god's spirit, yes? And that of Mythal's spirit/magic? Could be a connection to using the Dread Wolf's unique power, which would mean standard people couldn't remove vallaslin. Or it could just be your standard magic. I dunno. -shrugs-
---> Wouldn't it be fun to theorize who Mythal's betrayer was, and maybe they locked -that- power in to the orb? My money is on Elgar'nan!
---> Just throwing this out there since I'm commenting on other theories: what if the chant of light is a form of ancient elven magic, akin to the ones Solas mentions take ages to cast? If he was Shartan, as many theorize, he could have influenced this in Andraste. Then what magic does it do? Insert same questions for call of the stone/the song red lyrium spins/the calling/etc etc.
Or if you subscribe to him being Shartan, maybe he trusted in people before and was betrayed (ala Maferath, ala Mythal's killer). So him being uber secretive this time around would make sense. Uh. This is more of an answer to myself since I asked why not tell her the truth, earlier. :>
Carry on, carry on.