Sirius switched modes, from about him to about Peter. Just as Peter had been a good friend to him, Sirius was going to be in return. It wasn't about just one of them, their friendship. And he liked that. Honestly, Peter's statement didn't surprise him. From what he had seen of Peter, sometimes just in public comments on the journals, it looked like Wormtail was moving on from that worry of whether or not he was still married to Petunia that felt like ages ago. It was a different Peter. And that meant a different relationship. And not all relationships lasted.
"You've grown, and it sounds like you've grown apart," Sirius stated without judgment. "You've got to do what's right for you," Sirius spoke, "There's always compromise in marriage, but if you compromise yourself, how can that be a marriage?" It wasn't a rhetorical question. That seemed to be what Peter had been thinking about. The question didn't have to be answered, but there was a lot going on, and Sirius had some ideas forming, but they were possibly the wrong ones.