As mentioned earlier, your ex girlfriend isn't in love with this guy, and in all likelihood, they're probably not compatible anyway.
It didn't take her long to find him or jump into his bed, so there really wasn't much time for her to determine if this guy was right for him.
Whether you're single or in a relationship, certain love-life experiences are like rites of passage.
Some of them are exhilarating, like when you finally feel comfortable enough to be your true self because your partner is so all-in, watching you wax your mustache won't change a thing.
Others are less positive, like when someone might as well physically rip your heart out to match the emotional damage they're inflicting.