For a moment Harry frowned. Not exactly sure what Sirius was apologizing for. However, he was struck with a bit-and rather rare for a fourteen year old-of insight. Deciding now probably wasn't the moment to get into it. In fact, right this moment Harry would be fine with actually not knowing whatever Sirius was apologizing for. He just wanted this moment. This moment was good, he didn't have much of these. So it was alright, he was alright with not asking further explanations. "It's alright." Harry replied, sincere.
"It's alright." Harry repeated, grinning crookedly as Sirius looked him over. "Just don't make a habit of it." His own tone teasing before he sobered slightly. "I've missed you too." While the gap between when he'd last seen Sirius and Sirius had last seen him greatly differed, it didn't make Harry's words any less true.
He looked over at Remus briefly, "The both of you." He hadn't wanted Remus to leave Hogwarts and he hadn't wanted to leave Sirius behind, even though that'd had all ended up alright .. for the time being.