Unicorn, your issues with the partner of the guy you are interested in is what make (potential) triads so scary to me.
I've had so many female platonic friends whose husbands were douches (more conservative than their wives, or less respectful, or arrogant, or bad communicators, etc etc). I've had a few male friends whose wives I could barely stand, or who just bored me.
So, in a potential romantic situation, I feel that there is a minefield there. Sure, the couple might get along great, and viewing their love might give you warm fuzzy feelings. But it seems so rare that you will love both of the couple equally and that they will both also care about and desire you more or less equally. Sounds like the proverbial needle in a haystack rarity to me. If that is what you feel you need, I wish you luck on what will possibly be a long hard quest.
Love withers under constraint; its very essence is liberty. It is compatible neither with envy, jealousy or fear. It is there most pure, perfect and unlimited when its votaries live in confidence, equality and unreserve. -- Shelley
Mags, F, 60, poly-dating, loving and living with
miss pixi, F, 38
Punk, 42, M (dating since Oct 2015)
and a few more casual relationships