I am a huge culprit of performing this. Theres always one main guy or two that i can see a future with but keep one on the back burner just incase. There are a couple of signs to watch out for. if you try to make plans and she says, "Sure" or "We'll see", "maybe depends on my girl friend." then there's the random texts. This is when i have a lull in texts from the guys i want and need that extra boost. So maybe after a couple days text the buffer for that boost. She very well could not be looking for a relationship though. If she just wants to play the field and says shes not looking for anything in particular keep your guard up.