"My closest friend for most of my life." Cassian suspects Poe won't have the same reaction to that most would: pity, namely. Which he appreciates. If he deserved having pity in regards to his friendship with Kay it should be because of how Kay was, not because he'd been a droid.

At Poe's lip twitch Cassian lets out a little snort and glances at the droid. "Did you now? Good job."

How's that song go? Fuck the police.