Your girlfriend needs to chill out and just accept your honesty for what it is which is a guy trying to be genuine. I think many women, knowing their own base nature and knowing that most men are base at heart too, have a very hard time when they come across someone that is genuinely honest. All you can do is be open and if she has a hard time dealing with that then that is her problem. I wouldn't change anything just to make her happy. You can't dump your best mate because of an irrational woman.

Be a man and stick to your principles.