I am not sure myself but Im pretty sure it means that because they arent lovers she doesnt want to do more "bdsm" stuff so that she doesnt seem too eager/ make Io unconfortable?
Misa was overwhelmed by emotions that she just want to savour and make love to Io that night, no BDSM . ThatChrisss
And why did apologize and stop? That's what I don't get. Cause they would be lovers if they do that? They can't have vanilla sex cause she will catch feelings (she already has lmao)
I think I'm dumb but I didn't get the vanilla sex part