How to go on vacation with BF

I'm gonna be 21 years old and I want to go to vacation for my birthday with my long time boyfriend but my parents are a bit on the conservative side and they will not allow it-- Unless I'm married to him. 
Is there anyway I can get away with going to vacation without them finding out that I took him with me...? 
Please don't tell me that my parents know best or that I live under their roof or it's their rules.