My boyfriends sister is getting married tomorrow night and tonight is the rehearsal dinner at my mother in law's. I'm not sure if I should show up or not... I feel strange showing up and not being in the wedding yet coming to the dinner. What should I do? Should I arrive to the dinner with my boyfriend or should I stay home? Not sure what to do. I did not receive an invite only by my boyfriends word-of-mouth.  Thank you