I mean, saying you had a one night stand while doing it with someone else ... most people wouldn't like it ....
Good for Ryo for establishing boundaries ... Now it's up to Sera ...
It's true that they never established exclusivity with each other, but maaaaaaan I love to see Ryo was the one that fell for him first. It do hurt to see him feel physical pain at the thought of Sera holding someone else though :[