I think choosing the dark side of the Force in order to do something for the greater good, thinking you could control it, and then ending up being controlled by it instead
That really isn't too far from what we got - you just have to replace "the greater good" with the selfish desire to preserve Padme's life ( which is still a goal we could refer to as "good", in and of itself, given that she was a decent person, aside from the question of her value to the galaxy as a whole, whatever that might have been ).
Did she not understand what "killing younglings" meant? Maybe she thought he meant he "killed" - as in downed/drank - a few Yuenglings, instead?
Though he doesn't outright deny it, he also never admits to her that he killed the younglings, for whatever that's worth. He attempts to portray the charge as Obi-Wan trying to turn her against him.