Sirius wanted to press a little harder, to find out for sure whether Reg was involved in some of the terrible things that had been happening around the school. But their truce was still very fragile, and he didn't want to push the kid away. Better to wait, to get his trust back, before really digging. And if he was in trouble, Sirius was more than ready to get him out of it.
"Life with Mummy was always so fun." He noticed that Reg didn't take him up on dinner, so he let it slide. "I'm heading up to the Hall, but I get it if you're not ready to come with me. We'll keep in touch though, yeah?"