To get Therium, I had to choose the not obvious option when it asks you to talk to Tate, Aiden, or Dallan at the shard meeting. I cant remember what it is. Something like "leave the room." You do that and end up finding Therium. I really wanted Therium my first time through but ended up with Dallen because I couldn't figure it out. Next time through, I chose the leave option and ran into him.