The actor began dating the 'Horrible Bosses' actress earlier this year and while there have been reports the smitten couple are set to tie the knot, his pal Craig Wedren claims it won't happen.
Craig insists Justin - who was with girlfriend Heidi Bivens for 14 years before reportedly leaving her for Jennifer - is not the marrying kind as he doesn't like to be tied down.
Craig - who composed the music for the film 'Wanderlust', where Justin and Jennifer first met - said: "Justin will never marry her. He's not the marrying type - as you can see from the 14-year relationship he was in that didn't end in marriage.
"He is not the kind of guy to be owned."
He says Justin, 40, and 42-year-old Jennifer are complete opposites of each other and can't see them lasting.
He told InTouch Weekly magazine: "Jen is the complete opposite of Justin. She's all about Malibu and shopping and trying to stay young while Justin is about being an artist.
"The last place Jen would want to go in New York would be a dive bar."
The composer also claims Justin was "very taken" when he met and fell in love with the former 'Friends' star.
He added: "He totally lied to Heidi and broke her heart."