The 30-year-old met Mila on the set of Friends With Benefits and is said to have become 'infatuated' with her.
A source told Now, 'Justin's infatuated with Mila. He was the one who pushed for them to present an award together at the Oscars.
'He pulled her aside for a chat before they went on stage. He told her how he felt about her and asked if she felt the same.'
Twenty-seven year-old Mila is said to have replied, 'I'm not stealing anyone else's man - we'll be friends until you're single.
'That was the spur he needed to split with Jessica as things had been bad between them for months.
'He believed they both knew deep down it was over, but he didn't want to hurt her.'