Certainly we have witnessed this act by ladies. A lot of girls do not stand at a distance and watch the boyfriend and their best girlfriend cruising life.
The reasons while they 'snatch' includes,
If she finds the guy caring and loving she would most likely get jealous....especially if she is single or her own BF is not as caring and nice.....So maybe you should stop telling your friends just how caring your guy is.
She could actually fall in love with your BF,...yea...as they say, ”Birds of the same feather flock together” she might just like the same type of guys you do.