I mean, of course, if he/she went with another man/woman (not friends or family) when you made it clear you are free that night.
Select age and gender to cast your vote:
I am not talking strictly about someone you are in a relationship with, it could also be someone you are interested in.
I mean someone who shows interest in you too, not a random crush who may not even have an idea you like him/her or who never showed you interest. The point was the question is not stricly about your partner, but more about someone you are dating but you are not official.