But is the MC in a dedicated relationship with any of them?
Not really, no. The closest currently is Alice and Juliette, and even when Erik's "courting" Astra, she's perfectly fine with being fucked in the ass by Krowly before and after she and Erik start getting together.
You've got to understand that this a world where women give titfucks as a friendly greeting to their husband's friends.
We know this because Jill and Krowly reminisce about their mother doing that.
There's no real monogamy in this game world, to the point that there's hints at internal unrest within a religious order over attempts to become more "puritanical" - Nuns no longer getting anal to "help" people that need to get off.