Obi-Wan thinks of his own childhood, raised in the Jedi temple, never really knowing his family. He thinks of Luke, raised by his uncle and aunt, who have already begun to make it clear that they don't want Obi-Wan to be too much a part of Luke's life. Owen in particular seems to believe that if they ignore Luke's parentage, he will continue to be a typical, average boy.

"I believe we all wish that, once the time is past to be able to change it. But you have memories of her, and that's something to be thankful for."

He's often wondered if some of his own quirks were inherited from his family, or if he'd picked them up from his Temple family instead. Many people over the years had commented that he'd gotten his stubbornness from his Master, but was there more to it than that? It also worries him that perhaps Luke will have inherited some of the darker aspects of Vader (he would not call what was left of him Anakin - that was not Anakin any longer). He worries that in leaving Luke untrained and ignorant, he is setting the galaxy up for an even greater evil.

Which is certainly not something he's going to confide in Padmé about.