Aug 13, 2011 12:41 GMT  ·  By

Kat Von D and Jesse James broke up shortly before the day they were supposed to get married, citing distance as the cause their relationship wasn’t working anymore. A new report suggests Kat might have cheated on Jesse, which led to the breakup.

At least, Jesse believes this to be the case, an insider says for the latest issue of Star magazine (story via here).

Not only does James believe that Kat was unfaithful to him while they were still together, but he also thinks he knows who the other guy is: Kat’s good friend Bam Margera of MTV’s “Jackass.”

“Jesse believed Kat had been getting it on with her longtime friend Bam Margera, and they had a huge blowup over it,” says the spy.

Jesse’s reaction is ironic, to say the least. “Given his past history with Sandra, Jesse’s over-the-top jealousy when it came to Kat is almost laughable,” the source underlines.

“Jesse lives in Austin, and Kat’s based in LA, where most of her best friends are guys – many of whom she’s been intimate with in the past. There was always a lot of fuel to fire up Jesse’s jealous nature,” the insider goes on to say.

As if Jesse’s jealousy wasn’t enough, there was also one particular incident that precipitated the breakup, when he came over unannounced and found out that Bam had spent the night with Kat.

Jesse flipped, says the same spy.

“Bam went over to Kat’s LA home to hang out and talk, and he ended up spending the night. Jesse found out and questioned her about it, and Kat let slip something about how ‘Bam just can’t sleep alone’,” the insider explains.

“Jesse hit the roof when he heard that and accused Kat of cheating on him. They were barely hanging by a thread by then,” the source adds.

Considering that, before the breakup, Kat and Jesse swore to everyone who was listening to them that they’d been made for one another, it’s no wonder rumors of cheating emerge to explain the shocking breakup, word online has it.

As far as they’re concerned, Kat and Jesse are (for now) keeping mum on the topic.