This is a good opportunity to begin planning your life-long revenge on your brother. May I suggest beginning by dropping a steamy turd in his pillowcase?

time for you to plot a little revenge OP, sweet delicious revenge

Some family you got there. Good riddance to bad women OP. I wouldn't even justify it with a talk with her. She's obviously not worth your time, and neither is your brother. I think anyone capable of betraying their family willingly for 3 months isn't family at all. He made it apparent an easy lay is more important than you, so I would cut them both out of my life. Don't let them pull the whole moment of weakness crap on you either. No moment lasts that long.

should have kept her in a cage

At least you have a wicked cool guinea pig to keep you company when you dump your cheating ***** :)

Its probably because you have a Guinea Pig

If she sounds like a guinea pig, are you really on the losing side there?

You can find someone who will be 100% faithful to you! Keep your head up OP:)

How did you find that out? Or should I not want to know

I am sorry to hear this OP. Family should respect you and who you're with. I hope you two weren't very serious for your sake.