Oh MY GOD< im sorry but i am in almost the EXACT same situation!!!!!!!!!!!!!!!!! My house mate/best mate has completely dumped me and all our other friends, for her boyf who lives 2 hours away from us. She has had a complete change of personality, shes gone from a lovely caring person to a selfish, disrespectful one! She doesn't even sleep at home, she sleeps at her mums but pays rent at my place. But i cant say anything to her cos she will just cry and play the victim, I have made a few digs to her, like how i value my friends and would NEVER dump them for a bloke, but she doesn't seem to catch on.She genunilly thinks that she hasn't done anything wrong! anyways, What i am doing is just moving on, let her make her own mistakes, she'l come crawling back when it all goes t!its up (and it will) and she's have to work VERY VERY hard to gain her mates back again as it is hard to forgive her actions.
Show her how much fun you and your other mates are having without her.