Replying to Ladies tryin to make moves when you have a girlfriend

as if it is tough enough having a girlfriend be 7 hours away, girls are always tryin to move in on you at school. feel like a dick sometimes because i try to ignore them, but anytime you try to be nice they think you are interested and as soon as you tell them you have a lady friend they act like you did them wrong. anyone else get this or feel the bull sheet happening around them? i feel like i should be getting respect from the ladies if anything for being loyal when i could be running rampant.