I imagine them doing it and Sena trying her hardest to be his favorite by riding his dick while proclaiming that from now on he's only allowed to look at her...
...She really didn't notice that they were both awake and having sex under the covers? Well that's fine too I suppose.
I really like these stories that involve the girl night creeping on the guy just because she can't muster the courage to confess, though.
Interesting ending though. She might have been joking, but I'd be interested in seeing her...join in.