"Love gets people killed." Anything, in Dean's eyes -- got people killed if they were stupid about it. Brotherly love got him killed on more than one occasion. And it was just turning into an endless cycle of death at this point. He wanted to be angry at Liv. He wanted to push her away, but took comfort in this.
"I have done the same for him...and it got me killed. More than once so he knew what was going to happen. It always does. Which why it was stupid for him to get her involved. One of the stupidest things he's done to date." The stupidest was: Anything in the year of 'I dated a demon bitch'.