Drama! One Direction heartthrob Harry Styles and Taylor Swift had a notoriously bad breakup, but sources say he was trying to win her back recently ... until he got with Kendall Jenner.

Apparently Hazza has been sexting Swifty! Scandalous!

“Harry has been sending Taylor sexy texts for months," a source told Hollywood Life. "Most of the time she just ignores him, but she’s lonely and she still has feelings for him so you can’t really blame her for getting sucked back in.," the source added, noting, "He’s very persistent and very charming."

The insider revealed that Swift is "falling back under his spell," but that all changed once a certain "Satellite Kardashian" entered the picture -- and Swift is getting really nasty with it.

"Taylor still has feelings for Harry and he’s been totally leading her on," a source said. "She expected him to be chasing her down when he came to LA a few weeks ago, and instead he went after Kendall Jenner. It was a huge blow for Taylor. She and Harry were talking before he came to LA ... he didn’t make plans with her but he really made it seem like he was all about her so it really, really hurt her when he took Kendall out instead. That’s why she iced him at the AMAs."

It's all making sense now! The source added, "Taylor doesn’t get why Harry would pick Kendall over her, especially because he’s always made fun of the Kardashians. Taylor’s not a mean girl, but she can be catty at times and this drama with Harry is not bringing out the best in her."

Yikes! Here's hoping everyone moves on. T-Swizzle, there are millions of boys after your heart. Find a guy who won't break it!