Calvin Harris: Betrayed Over Taylor's New Hookup ... Suspected for Weeks Before Breakup

Calvin Harris suspected something was up with Taylor Swift weeks before their breakup ... and his suspicions were confirmed Wednesday when pics surfaced of Taylor making out with Tom Hiddleston ... this according to sources connected to the former couple.

Our sources say Taylor and Calvin were in a "committed relationship," but he suspected something was up in early May ... a month before their breakup.

As we reported, at the time of the breakup Calvin posted there was still "a huge amount of love and respect." Hours after the photos surfaced Wednesday, Calvin deleted the tweet.

We're told, "He's pissed and feels betrayed by her."

Taylor and Tom were out May 2, dancing at the Met Gala ... Calvin and Taylor announced their breakup June 2.

Calvin was mum Thursday. As for Taylor and Tom ... another song in the making.