The Saturdays singer split with her US producer boyfriend Jordan Omley last month and following their separation, she has grown increasingly close to the hunky model, who she dated for 10 months two years ago.
A source said: ''Mollie and Jordan are all over. It ended over a month ago and was actually very amicable.
''It was a mutual decision between them and things had just come to a natural end.''
Earlier this week, Mollie, 27, and David, 34, were spotted holding hands on a night out in Fulham, west London, but they are said to be taking their rekindled romance slowly.
The source added to The Sun newspaper: ''David and Mollie never fell out and remained pretty close even after they broke up.
''There's obviously a strong attraction but they're taking things slowly and waiting to see if it's practical to become serious again.
''But there was no crossover between Jordan and David. Mollie's a very loyal girlfriend.''
The 'Disco Love' singer is said to have ended her romance with Jordan because the distance between them proved too much, and is so private most of her friends only found out when she attended bandmate Frankie Sandford's recent wedding to Wayne Bridge alone.