Imagine if you went to McDonald's a lot and ordered a Big Mac Combo meal. A Big Mac, Large Fries and a Coke. You really like this meal. One day, you pull up to the drive through and order the Big Mac Combo meal and the girl tells you, "I'm sorry - you can have the Big Mac and the Coke, but you can't get fries with that anymore." You think about this for a moment, and sure - the Big Mac is the centerpiece of the meal, but McDonald's has some really good fries and you like their fries with your meal. So you say, "I've been able to get fries with that before, why can't I have fries with my Big Mac combo anymore?" The girls says, "Well, I just think it is better if you only have the Big Mac and the Coke from here on out."
At this point, a lot of guys are going to go to Wendy's or BK and see if they can get fries with their combo at that drive through window. But there are some guys who REALLY like McDonald's Big Macs and they might think, "If I keep coming here and ordering the Big Mac and Coke, maybe she'll change her mind and give me some fries with that later." So they will keep on getting the combo without the fries until the deal breaker happens: One day that guy is going to order the Big Mac and Coke and then he's going to pull up a little bit to pay, and someone else is going to pull up to the drive through speaker and order the "Big Mac Combo" and he is going to hear the girl say, "Would you like fries with that?"
That's why guys don't like to be friends with a girl who breaks up with them.