Grinding is annoying me?

I need some addvie my girlfriend and aye have been going out with each other for 8 months and she has just came back from holiday in dominican republic she told me other boys were grinding on her on the dance floor and she let them but afterwords felt bad but then she was convinced by her step sister it wasnt bad so she carried on to let boys grind on her other nights on holiday i was really upset about this because when i went to a club when she was away girls tried to grind me but i walked away i just feel grinding is not appopiat when you have a boyfriend/girlfriend is it wierd im annoyed