She's open-minded and adventurous? Heck, I would just lay it all out on the table, everything you've told us. She'll probably appreciate directness rather than games. The new gf *is* a cause for concern, since you don't want to get sucked into drama. I guess it depends on *how* problematic a person she is. Like, if she's scary-crazy or abusive, it would be a deal-breaker for me to have someone like that as a metamour (partner's partner).
The major players. Me, 30ish bi female. Gia, girlfriend of 4+ years. Clay, boyfriend/dom. Davis, ex/friend/"it's complicated." Eddie, roommate & fwb.
The supporting cast. Eric, Gia's husband. Bee, Gia and Eric's toddler. Dexter, Gia's lover. Helen, Eric's lover. Izzy and Nikki, Clay's partners. Liam, Eddie's husband.