I wonder if he would have explained things if he'd gotten the orb--perhaps he would have then had some means to share immortality with Lavellan. But even if he had, he had to be thinking that Lavellan would never, ever accept him as Fen'Harel. And considering what he said at the ball, he's clearly not asexual. All that time spent yearning, wanting... and knowing if he did, he'd be making it even harder to leave when the time came. The time was going to come, sooner or later. He would have to leave, and, well, Uth'Shiral is mortal. It wouldn't be easy to watch her grow older by the day if he couldn't do anything about it.
I still feel sorrier for Lavellan, because Solas promised to explain and he didn't. He led her on, when he could have simply said "No," from the beginning. He didn't even leave a note for her wishing her goodbye.
But, for those who've also seen the ending cut, I wonder what will happen now that Mythal/Flemeth is part of Solas/Fen'Harel? Not to mention the Old God Urthemiel. Some think he's up to no good, but he said he was off to help the people and I am inclined to believe that's his actual intent, given his actions throughout the game and the fact that he seemed to like it when you helped people (elves specifically). And yet he seemed so miserable over the orb. What's its significance? Also, he really didn't want you to use the Well, but if you did... well if Flemeth is a part of him, the Inquisitor is now bound to him in that respect as well.
Something else that I've been wondering that I think might be somehow related to Solas: Solas/Fen'Harel was apparently asleep/wandering the Fade until the beginning of Inquisition. Was he Felassan's master? Corypheus was not searching for the eluvians at that time. If so, then why did Solas need the eluvians and why did he murder Felassan when it would have also suited his purposes to have Briala take control of the eluvians? My theory is that it wasn't Solas or Corypheus, but whoever it is, is the reason that Fen'Harel, Mythal, and Urthemiel are teaming up.
I'm also deeply concerned about that orb, because both Solas and Flemeth seemed to think it was a terrible thing to lose. What was it meant to do?
I would love to see the Inquisitor able to tie up loose ends with Solas, would like even more for him to permanently return to my party. But I can't foresee any further romance content, unless Solas decides suddenly that he needs an Old God Baby or something.