Partner is not in too deep and she's willing to pull back for your well being and the well being of the relationship of (you + her). You state you don't want them together. Those things line up... so why not go with it?
What's so horrible about saying "Hon, thanks. Since you are willing to give it a pass? I'd appreciate you giving this one a pass then. I'm just not feeling great about this one." If the goal is a shared harmonious polyship -- don't be signing up with people you already know you don't get along well with. That's not upping the odds of success for the new polyship.
And thank your partner for her willingness to hear you on that and consideration of you.
Some people are just "messy people." Too messy to date/polyship with. Maybe people like your boss, your parents, etc. Maybe she's on your "messy people" list.
Doesn't have to be a bigger thing than it is. YKWIM?
Last edited by GalaGirl; 04-15-2013 at 05:46 PM.