"We all changed," he said with a sigh, breaking eye contact with Bellatrix. Her slight frustration did not phase him in the least. Rabastan could say a lot worse to Bellatrix without her even batting an eyelash (or at least he assumed) and the same for her.
He appreciated her attempt to give him some dignity and honor. Rabastan spent those years exploring himself, spending more and more time believing everything his parents told him. He allowed himself to give into them and to accept that he was rubbish. Somehow, though, the Dark Lord believed him and accepted him. Rabastan believed in his purpose, his mission, and everything they stood for. He worked hard to get to where he was, and then to be thrown in Azkaban. Was this all a joke? But even the Dark Lord would not have pitied Rabastan, he could see better than that and knew Rabastan well enough.
Almost correcting her by saying 'if you were going to do the opposite, you'd've married me,' he refrained. Bellatrix probably knew, well enough, what ate at Rabastan's heart all those years, but now his heart was filled with anger, vengeance, and justice.
Suddenly curiosity struck him, "then you do not love my brother? Did you ever?" Purebloods did not necessarily marry for love, but he did not take Bellatrix or Rodolphus to be unfaithful. Rabastan was not privy to their endeavors, so he likely knew far less than he assumed.