He knew he wasn't being fair by using logic with a Slytherin, logic that hurt but was nonetheless valid. Cass wouldn't be able to attack what he was saying, not on an intellectual level, but Percy wasn't stupid enough to think that Slytherins had no feelings or that they couldn't be hurt by what logic hid. Those were stupid notions for school children and he hadn't been one of those for too long. Still, knowing didn't prepare him for the reaction he actually got.
"Breathe. Cass, come on, you need to breathe. Dying now is not an option." Not after waking up after three weeks in a coma.
Percy kept brushing Cass's hair. "It's a good solution, Cass. She cares for you; I know she does, and she'd take care of you even if she's a bit insane, but you seem to like her. You like her enough to have sex with her," he added. "It gets Lestrange off our backs. You go back to work. We're better off this way." He'd go back to being alone, because at this point, it seemed like the only (and somewhat preferable) solution. "I'll be all right."