I have a very soft spot for Vigil. I also had some troubles thinking about his character, how he'd react and work within the dynamic of an open-relationship when he's a pretty protective (if not somewhat possessive) guy. He's also monogamous himself. That being said, the relationship between him and Lucian is really good. They're very upfront about any issues they have, jealousy, possessiveness, etc. It isn't perfect from the get go, but they're always open and willing to learn. All in all, they adore each other in their own ways. Vigil also gets along well with the others of the main cast as well as the secondary characters.
I know I put his kinkiness up halfway but the majority of that really is just him liking to bite and get rough. He's an overall pretty vanilla guy actually. Surprisingly more romantic leaning, wanting the experience to be more about the exploring the other person's body and enjoying it as something that enhances their relationship. I don't know if that made sense, but basically he's a big sap at heart though he certainly isn't opposed to doing things purely for pleasure.