Unfortunately, it's off-again for on-again, off-again couple Shanna Moakler and Travis Barker.  They announced their plans to marry again last month.  Yet after having an argument so bad that the police were called, the couple decided to call off the wedding.

'Travis confronted Shanna about her having an affair with Gerard Butler while he was in the hospital recovering,' the source says."

Travis' camp said he has reached the end of his rope.

Barker's rep tells Us: 'After surviving the plane crash his
driving force in life is the love he has for his kids. He is tired of
all other drama and is ready to move on.' 

'The babies are the most important thing right now,' adds the insider. 'Shanna cheated on him and then told everyone they were in love again
while she was having an affair and he was recovering from the accident.' "

Shanna's rep has a response to that.

They did break up but Shanna never cheated on Travis while he was in
the hospital. Furthermore, Shanna is tired of playing out their
personal relationship in the press."

Sometimes things just don't work out.  Travis and Shanna originally divorced in 2004.  They have two children together. 

It's unclear when the break-up occurred, but if you check out the thumbnails, Shanna looked like she well into the "getting over him" phase with a mystery man (not Gerard Butler) while celebrating her birthday last weekend.

Photos by Wenn.com