Severus wasn't in the mood to argue. She had no idea how 'in-tuned' he was to the muggle world. No idea.
"You're right," he took a puff and then offered her his fag. "Would you like a filter for your second hand smoke?"
He blinked disbelievingly at the web of lies Sirus had woven. What the fuck was that man's problem? Alive or not, Severus suddenly felt like hexing his bollocks off. And then it hit him-Sirius had called Marlene the love of his life. Marlene. Severus' Marlene. If anything she'd been the love of his life. Hell, he hadn't hardly looked at a woman since she'd died. Sirius had bedded countless women-and probably a couple men, too.
He realized after a moment he was sneering so hard he was close to bearing teeth and quickly shut his lips together tightly.
"I did no such thing," Severus said through clenched teeth, somewhere between an angry growl and a bitter grumble. He shifted a little uncomfortably. "They fucked. Once. Then, it was over. Later she and I became involved for..." Merlin, how many years? Not that it was Tonks' business. "...quite some time. There was no magic involved and your cousin is a dead, dirty liar who I could kill again for that comment."
Maybe he'd throw in a couple 'crucio's as well....