After all, the last time they had been together, things had not gone well.
"Then neither of us is the same man from that day. But you must forgive me if I am still wary. Though I have no desire to destroy you, I am not without some vengeful feelings."
And that was extremely difficult for Obi-Wan to admit. Because that meant that he, too, could be vulnerable to the Dark Side of the Force. Just as any other Jedi was.
And Obi-Wan wouldn't argue that Mustafar hadn't changed him. It had. And not entirely for the better. He'd become isolated from part of himself and from those around him after. He supposed there had been some benefits to that day. Something to gain. Some knowledge of himself and of the Force. But he still hadn't figured it all out yet. That would take considerably more time.