Calvin Harris: This is What You Came For ... The Cheating Song!!

The song Calvin Harris wrote for John Newman -- which Calvin says chronicles a love triangle between him, Taylor Swift and her new BF Tom Hiddleston -- just dropped ... and it sure sounds like a play-by-play.

TMZ broke the story ... Calvin wrote the cheating song "Olé" from Tom's POV. But Taylor's camp's calling BS ... saying Calvin wrote the song long before she hooked up with Tom.

The lyrics we said would be in the song are there ... with Tom's famous 'Thor' character, Loki, kicking off the song -- "Low key you won't tell none of your friends about me."

And ...

-- "You've hidden my name in your phone so you can call me to tell me you've been going through hell. Left him alone and you booked in a hotel."

-- "I see online that you begun to be a good girl and take trips with your boyfriend. Being attentive, continue to pretend ..."

Sounds like a hit!