'Sickening' would not have been the word Severus would use to describe the change in Tonks' appearance. In fact, he'd always found Narcissa to be quite the attractive woman. Upon noticing the resemblance, Severus blinked in the sight, a bit shocked. It was uncanny. He could easily be looking at a large picture of the Black (now Malfoy) sister from years ago.
However, when Tonks spoke, the resemblance lost its original charm, and the slight shock on Severus' face changed to annoyance once more.
"As I said, Miss Tonks, Sirius would have escaped at some point, regardless of who was or wasn't there to stop him. Why can you not just accept that he died for something this way? He was trying to save what was possibly the only good thing in his life. God knows I hate Potter but that man loved him and died trying to protect him. Nothing could have kept him in that night, not even you."
Since Sirius had died, Severus had realized how much respect he had for that man. He had the courage to always fight for what he believed was right, something Severus had often lacked throughout his life. Hell, he'd been to Azkaban, and come out half sane. That was an accomplishment, no matter how annoying you were.
Not to mention, although he'd never admit it, Severus kind of enjoyed bickering with that arsehole. When Sirius wasn't purposely trying to anger or dual him, they would get rather witty with their remarks sometimes. He'd gotten quite good at it in his old age, unlike when they were in school, where every remark was immature and unintelligent.
"Even if I were homosexual, I can assure you Remus would not be my first pick. He's all yours, don't worry."