Sirius didn't need to be told twice. He had been wanting to sit in on one of the Potter lunches since they started, and had a feeling they didn't happen in Gryffindor tower specifically so they Sirius wouldn't be underfoot. He knew why, obviously. As much as he wanted to be he wasn't a Potter, and they clearly had a lot of their own stuff to work out. But if Lily wanted him there then he would go. At least once. He hoped he'd be self aware enough to tell if his presence wasn't welcome.
"Then I'll be there with bells on."
He couldn't really imagine what it would be like to have children, let alone a son that was older than you. Only in this crazy world could that be a thing.
"It's a lot to take in," he agreed. "I, um, I was thinking that this might be the universes way of giving us a, well, a do-over." It had come up often enough. Second chances. With Remus. With Peter. But now with Lily here it felt like that might actually happen. "Maybe the castle is giving us a chance to start over. Do better. You know? Live the lives we never got."