I don't think their a couple, most likely friends with benefits or an entanglement.
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They are fwb, never meant "breaking them up" as in them being a couple, but just their already existing relationship being altered. Once you go a route, they'll fall in love with your oc and likely end their fwb relationship. Also, according to his relationship chart, Ais has feelings for Vere, so I think it would be nice to have an option where your oc, Ais, and Vere can all be together.