Leon likes spending time with you, working with you, and being around you. He finally started feeling things again when you joined the Shadow Decree. He thinks it started when he noticed you keeping to his schedule and accommodating his OCD.

Talking to you made him need your attention. You and Hall are the only people he willingly takes time out of his day to speak to. He'll figure out how to ask you out as soon as he realizes the true extent of his feelings. He's getting there don't worry.