Should I give in to my girlfriends demand ?

If you could be more detailed about your situation I could help you with it. Otherwise, what I can say is if the demand isn't something you are comfortable with you shouldn't have to "give in" to a demand. If it's something that truly makes or breaks for your relationship, you have to know how far you want to go for someone you love. How far they will go for you, and how the demand effects your moral code/ standards. If they are making you do something you're not comfortable with, chances are you shouldn't be with someone that will make you do stuff you're not comfortable with, unless that demand is something small/ petty and you've been in a healthy, lengthy relationship. only you can decide what you do.