My Brother's Girlfriend i think she's obsessive.?

My brother in which he's 19 and dating a 18 year old for the past month . every day i see them together from the minute i get home from school which is like 3:00pm to 4 am the next day. Everyday it's been like this. On weekends she is at our house earlier than any member of my family is awake except my brother and she comes at like 8:00am till 4 am the next day. I haven't been sleeping because of this. I don't like her because she took away my brother. He used to go on vacation with us but now he can't because he has his girlfriend and she doesnt want to loose her. Christmas time. He went to her house instead of our own. So christmas was a waste. I hate how she's always with him. When I had my Athletic Banquet which was 60 dollars for a person that isnt a member of Athletics and 40 dollars for athletic member. I myself had to pay both my brother and her tickets. She never said thank you. I regret for doing that. But i mean i was being a nice 14 year old i am. I wish she would stop staying hours. I really want to know what her parents are thinking. What do you think I should do. I can't stop faking it. It's harder than it seems. I'm usually kind and easy to talk to among her but deep down it's hard to talk to her because i never know what to talk to her about and i hate how she took things for granted.