I let Blackwall rot in prison so he will be dead. I got pissed that when I rescued him, commanded him to go to the Wardens, he STILL says at the end 'Im gonna stick around for a while.' umm how about you honor my judgement and gtfo jerk, just because I felt you were possibly worthy of redemption doesn't mean i want you around. So now I just let him rot.
Mhm, Lavellan rescued him and since she didn't like the Wardens, she told him to continue his lie. I mean, I roleplayed her as an astonishingly cunning Dalish who enjoyed the Game and wished to hide his crimes. Also, greater good before that one life he saved in Val Royeaux.
Needless to say, he wasn't pleased at all and didn't want to talk to her anymore: "blah this is none of your business I can't believe I was so much in love with you". I collected Warden's artifacts, took him to the Hissing Wastes where he actually told me a funny story - but back at Skyhold, he should have been named The Grumpy One, hehe.
That's when she switched to either Bull or warriorless party.