Melodic chirping pours through my shut windows.
A unicorn is rare, mystical, and perceived as a myth. In the non-monogamous (or monogamous) community it's quite the same. This is a term (that can be derogatory) used to describe someone, usually femme, who joins a couple for a consensual ménage à trois. Generally it's monogamous-ish and heterosexual-ish couples look for a bisexual female for no-strings-attached, usually one-time-only sex.
"Polyamory is not for everyone" is something I find myself saying often. It's a way to defend myself from judgement. Singling yourself out as an oddball, a sore thumb, strange. People are receptive, less judgmental.