At Slughorn's party, Hermione asked you to pretend to be her girlfriend. Just to make Ron jealous

You accepted, and everyone believed that you both were partners. Since you were supposedly couple. Everyone was begging for a kiss

"i-it's just a kiss... it's nothing... just a quick kiss" she said nervously and you consented. And both of you kissed

Both thought it was going to be a quick and simple kiss, but more time passed than they thought...