It's very possible that he's at least sympathetic to Dragon/Luffy and was once friends with the former.
Think about how he always lets Luffy go. Kizaru quickly heading for Sabaody could be reframed as him trying to get to Luffy before Akainu could, so that he could give him a chance to escape.
This would also explain his uncharacteristic irritation after Luffy escaped.
Also in MF he shoots the key instead of Luffy and even kicks him to the safety of WB's arms after he gets mobbed by VAs.
He completely misses Law's sub and even says that if they escaped it would be due to luck. Then there's EH where he fed Luffy.
IMO what originally happened was that Akainu/Kizaru/Dragon were a trio in the Marines, but Dragon found out about the WG's secrets and defected, while Akainu/Kizaru were tricked into believing that the D clan is evil.
This caused Sakazuki to hate Dragon and commit himself to destroy the Ds while Kizaru became a depressed salaryman while hiding his true feelings.
But there's also a possibility of Kizaru becoming a traitor of some kind, because in Battles Without Honour, his actor inspiration's character was a backstabber and secret underboss who betrayed Bunta Sugawara's character.
BUT according to Oda Kizaru's main inspiration was another character, a detective named Borsalino 2 from Truck Rascals 2 and I can't find anything about him, so...idk.