why do women do this?

Yeah dude, it's not like she's going on and on about the guy she loves specifically to torture YOU. What an egocentric thing to think! She doesn't like you. She's not going to like you. Accept that. I'd also take others' advice and take her off your facebook, or if you don't want to do that, you can go into your preferences and choose the people you want to hear more about vs. the ones you want to hear less about.