Things are not amicable between Jennifer Lopez and Ben Affleck ... the lines of communication are closed and it's making it difficult to hammer out a divorce agreement.

Sources with direct knowledge tell TMZ … J Lo and Ben are not speaking to one another -- in person or over the phone -- and it's really slowing down their divorce.

Ben and Jen's icy relationship is really the only thing preventing this from being a quickie divorce ... we're told they have a prenup and the only asset they have to divide is their Beverly Hills mansion, which is on the market.

Our sources say J Lo and Ben have NOT hired lawyers and are instead having everything go through their respective business managers, who are trying to figure out the financials behind the divorce ... but it's complicated because the principals are not talking.

TMZ broke the stories  ... the estranged couple's Bev Hills estate is on the market for $68 million and Ben just closed on his own $20.5 million mansion in Brentwood, as Jen remains on the hunt for a house of her own.

Ben closed escrow on the house the same day Jennifer turned 55 ... that's just a coincidence, but we do know there is no love lost between the two.

Ben and J Lo will eventually hire divorce lawyers, and we're told no documents will be filed until they reach a settlement. They will file legal docs requesting a divorce, the judge will sign it and that will be that.