Most Helpful Guy
There's no commitment to a friends with benefits relationship as there's no emotions involved and both people are purely into each other for sex and nothing more. It would have been courteous of her to let you know she found someone else instead of ghosting you but either way, she's not obligated to be with anyone and can hang out with whoever she wants. If you two committed to being strictly friends with benefits with each other, that would have been a different story but it doesn't sound like that was the case. I would say this was shallow of her to compare you to her new friend with benefits like that but otherwise, it's just whoever she's more interested in since she's not in a relationship. Try not to take this personally and move forward with finding a new friend with benefits if that's what you want.
Most Helpful Girl
You were friends with benefits, not a serious relationship so I don't get why you'd call her shallow. It's her choice who to have sex with not yours. If this were a serious relationship then yeah I'd consider that shallow, but it wasn't.