Episode: 5.14 My Bloody Valentine
Castiel: your people call them "Cupid"...what human myth has mistaken for "Cupid" is actually a lower order of angel. Technically it's a cherub, third-class.
There are dozens of Cherubs on Earth as of now, according to Castiel, which humans refer to as "Cupid". Cherubs are very low on the Celestial Chain of Command, more specifically ranked as third class angels.
John and Mary’s marriage was 'top priority' on Heaven's agenda. Their marriage was orchestrated by a Cherub. And apparently, they could stand one another, but Michael had a cupid interfere, which resulted in their marriage.
It remains unknown as to whether or not cupids need Vessels. And how they manifest is also unclear.
We first see a Cherub - aka Cupid - in 5.14 My Bloody Valentine
Cherubs can bring couples together