to wear or not to wear

Recently went out with a guy friend and my girlfriend pressured me into wearing a revealing shirt, I'm not used to that but hey whatever! Shirt was normal except the the middle of my chest there was a oval cut to see my breasts, all throughout the night my male friend kept checking me them out and said sorry I can't help it they're just out there!
Now the question is: do you wear clothes to have someone stare out you? Is that like the "whole" purpose of wearing something? Or is my friend just a pervy virgin?