I know it seems somewhat confusing but it's rather simple.
Let's say one of your friends ask you to pretend to be their date to a party because their relationship with another person is hidden among their friends; After the party they plan to meet up and go out, Would you do it and how would you feel about it?
One of my best friends asked me this earlier today and normally I don't mind but I feel uncomfortable for some reason. I don't have any feelings towards her or anything.
... is she going to do other things too? lol If not, then no.
On a serious note... I probably wouldn't but only because if she has to be hiding the other guy from her family members, then that obviously means the other guy is no good for her in some way and I wouldn't go along with her simply because I wouldn't want her to get hurt by the other guy.