So what is the different girl endings a player can obtain? Also is it better to have Primrose as a girlfriend or friends with benefit?
At the end of the game, you're required to choose which love interest you're going to settle down with. Anyone who you romanced but do not choose, will be shown as heartbroken/weeping in the epilogue.
Unless you want to see everyone except your chosen unhappy in the epilogue (you monster), it's better to have FWB relationships (or just skip having sex with them entirely) rather than romances with all but your chosen love interest.
Primrose and Callie have both romance and FWB paths. (if you follow the FWB path with them, you cannot choose them in the endgame).
Samarra, Thorn, and Sister Agnes only have FWB paths (but you *can* choose them in the endgame).
Nell and Evelyn are the only characters who you cannot have sex with without romancing them. (so if you're aiming to avoid broken hearts, you must skip one or both of them entirely).
here's a list of all the characters you can choose to settle down with at the end of the game:
Evelyn
Primrose
Callie
Nell
Samarra
Thorn (the fairy queen)
Belle (your pixie sidekick)
Sister Agnes (only in a NG+ game)
There's also two threesome options:
A throuple with royalty
A throuple with Callie and Evelyn.