Completely ignoring the potential future they had together, he focused on the key parts of what she was telling him, and mulled it over. It was making him... irrationally angry. Or perhaps entirely rationally angry. He wanted to punch something, or kick something, and he found himself wishing for a full so that he and Sirius and Remus could go out and just sort of... tear each other apart for a while with good reason. Or at the very least valid excuse.
It felt like cheating. And the only reason it felt like cheating was because she told him that they had, eventually, gotten together. If he'd never known that... he probably wouldn't be as angry as he was now. As frustrated with the situation as he was.
"Glad to have gotten that off your chest?" he said coolly, before he got up from the chair, no longer wanting to be anywhere near he, turning his back and... well, really, wanting to storm out of the room but finding that too childish even for him so he simply stood there with his hands clutched into fists. "It is clearly no business of mine who you see. As you said, I'm too young to remember anything relevant. It's as if you found someone engaging in school."
It was on the tip of his tongue to dismiss her. 'If it's all the same to you, I'd rather not speak to you right now.' But... he couldn't bring himself to do it. This was Lily and she could... still do no wrong, in his eyes.