The complaints of a person in an unfulfiling relationship who refuses to leave, no matter how terrible they say it is. When asked, "Why don't you just..." it is frequently followed by the line "Oh, no, I could never..." (A very cyclical and rather hopeless situation, really.)
Derived from a song of the same name by "The Barstool Prophets."
I got a call from my ex last night; she just kept singing Robin's Song about her new asshole boyfriend...
"And as he stumbles towards her / Left hand raised / She sings Robin's Song" --The Barstool Prophets