Fowler allegedly sent text messages of support to the 22-year-old while he was in prison and comforted him when his wife Jade Goody passed away.
According to the News Of The World, Tweed and Fowler slept together following a night out at London's Faces nightclub earlier this week.
A source said: "Everyone knows Jack goes for girls with big boobs and after implants earlier this year, Maria fitted the bill perfectly. It was the climax of a year of sexual tension for both of them, and Jack told us he was all over her like a rash.
"They both had a great night and Maria was hoping they might have a future together. She'd fallen for him head over heels. Jack was initially really nice to Maria and seemed really pleased they'd got it on together.
"But that, and the fact he'd been so keen on Maria for such a long time, makes what happened next all the more cruel."
The tabloid reports that Tweed has now broken off his relationship with Fowler and decided to ignore the model after spotting her out later on in the week.
A friend of Tweed's added: "To be honest, it was embarrassing to be his mate, seeing how offish he was with Maria. This poor girl, who'd done nothing more than be a rock for him and then fall for him, was tossed aside as he went on the pull again.
"Maria's been lovely to Jack and wouldn't dream of going public about what he's done."