My brother's girlfriend is jealous of me?

AutumnsMonologue8
I was a little shocked when I was told this by a friend of mine. My brother is 5 years older than me and we're finally at the age where we are sharing friends. So naturally, we started hanging out more. We've never been close before, but our relationship has gotten better in the last year or so. We hang out every other weekend when I'm home from college and we formed a band together with some mutual friends.

A little over a year ago he started dating a girl my age that I went to school with. I didn't really like the idea because she had been dating his best friend and cheated on him before breaking up and moving on to my brother. Regardless I've been very friendly with her and try to cheer her up when my brother is playing games or off doing his own thing. (She gets really pouty when she's ignored and takes it out on everyone)

Our band had a show last weekend, which she went to, and afterward, my good friend told me what she was saying while I was on stage. She told her how she was jealous of our relationship and that Adam asked me to sing for the band rather than her. I guess I feel a little angry that she is trying to tear my brother and I apart after we're finally getting along. Lately, every time I visit from college, she claims the weekend as their "alone time" even though they don't do anything but sit around at her house. So finding out that she's jealous of me is a little unsettling and sounds ridiculous to me.

Anyways, I would like to hear your guys' opinions, women or men. Have you seen this situation before? Is it unsettling, or normal? Does it sound ridiculous? Whatever you would like to input.
My brother's girlfriend is jealous of me?
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