Sometimes R2 DT thinks back on how Anakin left him standing next to Padme. He doesn't understand why he didn't come back for them and why he never saw his best friend again.
Then he meets a cyborg, and he discovers that it isn't really a cyborg as he has done a scan and it reveals that it is more man than machine, and it treats him like an equal. He thinks he hasn't been treated like an equal since...
Since...
And so he starts to pay attention to how it moves, how it clenches his right fist, it's speech patterns, how it fixes things with that intuitive understanding and so he starts to think that the cyborg is a he, and that he is...
...not his best friend as he doesn't understand how the man that fixes everything hasn't fixed himself or how that life support hasn't been altered more to suit his needs. He, like so many others, just doesn't understand.
But he still catches the cyborg ,who he hears is called Darth Vader, looking at him more than is normal.