Attachment
Attachment was against the Jedi code. He was well aware of this early on, but he ignored it.
A child was always attached to his parent, even with in the Jedi order this couldn't have been all that odd.
That attachment could be excused.
He was a boy and latter a man, could it really be expected that he would not develop a childhood crush. She had been so pretty and the attachment had naturally developed early on. But he had push past it and concentrated on his training, though she was always in the back of his mind
That attachment could be excuse.
He had had developed friendships, as all children do. It is a natural part of the life, one needs interaction with other people if they wish not to crazy, and they need to be pleasant if the child wishes not to be sad. Friendships with then the Jedi order were common place.
That attachment could be excused.
But for twenty years he thought about the attachment that was wrong. His attachment that had brought about the virtual end to the Republic, the beginning of the Sith, the death of the order.
If he had not been so attached to Anakin, the fate could have been avoided.
He knew of his Padawan's attachment to his mother, but, he reasoned, he himself had been so very attached to Qui-Gon, Anakin's feelings were more then natural.
He knew of his Padawan's attachment to the senator, but, he reasoned, he had been attached to Siri once, a part of him still was, and their was no harm done.
He knew of his Padawan's attachment to his growing friendship with the Chancellor, but, he reasoned, he had many good friends from his young day that he was attached too.
Obi Wan was far to attached to Anakin to begrudge the boy any attachments of his own.
Obi Wan's attachment to Anakin had brought about the empire just as surely as Anakin's attachment to Padme had.