Ron kind of, sort of, stopped thinking. He'd never admit it to anybody {although he was sure they could guess}, but sometimes his feelings got the better of him.
He gaped at Sirius. How could he--this easily--Ron's family--"Fake it?" he stammered. Ron never faked anything. And Sirius had implied he didn't know his own family -- his own family!! Yes, he might not like them always, but. But. They were family.
He drew back his arm for momentum and punched Sirius hard in the face, hearing the man's nose going crunch against his fist.
"You pathetic little coward," he snarled, catching Sirius's shoulders and shaking. "You think everybody thinks about their family like you? That we wouldn't bother to know them??? You think we don't care about each other?"
He pushed Sirius away, and said, "You stay away from my nephew, Black, because if you come near him, I won't stop myself next time."