It sort of happens in a natural way, no one tells him, Malroth just feels really REALLY Attached to Shion a months after post game events. Shion had always felt the same [her feelings start at the Skelkatraz saga] but with Malroth not understanding love, she decides to keep them to herself and tease him with "i love you's" until one day he suddenly says it back and means it. The very last frame is a direct reference to their first ship piece.
“As her power for Creation grows, so too does your power for Destruction.”
Perfectionism was keeping me from moving forward when I thought of what he might say. He’d tell me to hell with it and draw as I see fit and stop worrying so damn much about it being perfect and to have FUN with it. So I did. He’s practicing to hone his powers too. It’s a struggle but he’s trying, we both are!