Once a man has enjoyed the pleasure of getting with a girl, a metaphorical shield, that prevents him from getting with any of her friends. This is because the friends are worried about said girl getting all upset. Of course, this "bubble" becomes obsolete once the girl has stated that she has gotten over said man. When the hell's that gonna happen though? Note that this may not solely effect your sex-life with her friends, as elaborate cock-blocks may prevent you from getting with girls outside of the circle
Male A: Hey, you tap Female A last night?
Male B: No man, ever since I got with Female B, there's been a romantic bubble of trust between me and her friends.
Male A: That sucks man.