The Girls Aloud star flew to Ibiza last week, where Crane is working, to try and save their relationship, but in vain, reports thesun.co.uk.
When Harding refused to answer her phone for three days, they decided to split.
“Sarah and Tom had a huge bust-up and told each other the wedding is off. Although they’ve always managed to patch things up in the past, it’s worse than anything they’ve gone through before,” said a source.
“They’ve been fighting like cat and dog. Their relationship has been strained because he’s been in Ibiza for the summer and Sarah was working here. They’ve always had a volatile relationship but this time it’s far worse.”
“If they do get married, they both need to start living their lives differently – and that’s not going to happen any time soon. It’s a shame as they do really love each other but pals can’t see how there can be a way back from this,” the source added.
Crane proposed to the singer on New Year’s Eve in the Maldives and she gave a nod without a second thought.