The pair announced their engagement in January, but it was reported last month that they had split after a huge bust-up.
Crane is now preparing to return from his six-month stay in Ibiza for a make-or-break chat with the Girls Aloud star, according to The Sun.
A source said: "Sarah fears Tom will say the relationship is off for ever. He's worried that they can't function as a couple.
"He's had plenty of temptation from other girls out there too. He and Sarah still talk on the phone and she tells him she adores him, but he's been distant."
Crane has previously insisted that the couple are simply on a break, with sources suggesting their April wedding will still go ahead.
Watch Sarah Harding performing 'Call The Shots' with Girls Aloud below: