Rarity is waiting for her true prince and husbando: me.
My absence makes her try to connect with literal princes and the like, but it never works.
Why? Because they're not me.
Season 9? That's just the timeline where I wasn't transported to Equestria.
Rarity ends up alone because I, her destined lover, never arrived.
The other Mane 6? They move on romantically just fine, because (you) were never their fated stallion.
Their true love is somepony else. Sorry your waifu cucked you, but facts are facts.