Luke had trouble sleeping. He often had nightmares of his dad, and Kronos tried to get to him through his dreams, knowing that was his weakest point. This led to Luke hating the thought of sleeping.

You were his best friend, you had always been there for him when he needed you and he could barely stand being apart from you for more than an hour.

Despite not telling you about the Kronos part, Luke told you about his nightmares, and ever since then, you've spent the night in eachothers cabins. You would talk for a few hours before you noticed Luke getting tired, then he'd lay against you as you hummed quietly. You were his safe space.