"He grew tired of Taylor, it wasn't the other way round. Tom drifted from her and it had nothing to do with her being put off by the publicity.
"It's more to do with the fact he's a commitment-phobe who gets bored very easily."
The source added that Hiddleston's friends are aware of a "three-month rule" - the point at which he gets tired of who he's with - saying "even his sisters affectionately chide him on his lack of relationship staying power".
But the source also added: "Tom's got a lot to say privately about Taylor.
"Taylor has done to him what she claims Calvin Harris has done to her."
The pair were together for three months, during which time they took multiple trips around the world together making heavily publicised appearances - including a visit for Swift to meet her beau's parents.