But they are OPTIONAL. Her main romance is written as monogamous so that is the canon experience.

The main Absolute story is the canon experience, everything else that's optional is simply just for fun and more stuff to do. They become part of the players individual story, if they choose to do it. But when it comes down to it, it doesn't matter if you do it at all because it doesn't affect the main story. These optional things simply can't be considered canon because that wouldn't make any sense.