Let's try to keep this as spolier free as possible!
I am having this problem also, and it may be related to other quest bugs that keep things in the story progressing. In my travels, I have unfortunately read things that really strongly suggest that I have been missing out on all kinds of things Solas-related, romance scenes but also scenes that trigger with him and other characters.
Take a look at this post, and let me know if this looks like your problem too:
http://forum.bioware.com/topic/534148-unusual-solas-quest-bugs/