They're now each accusing each other of having affairs, and that's not all - Heidi has gone so far as to hire a private investigator to spy on Spencer.
As we reported last week, Heidi is allegedly staying at the home of the hilariously named Cougar Zank, a Marine turned bodyguard and pal of Pratt.
Earlier this year, Zank moved into the home Spencer and Heidi were renting at his request, with Pratt claiming that the two were writing a script.
But when Heidi Montag split with Spencer in May, Zank invited her to stay with him at a home he rents in Malibu, which totally set Spencer off.
AT WAR: Is Speidi's split actually legit?
He considered Cougar Zank his friend, and is sure the only reason Cougar would have sided with Heidi in the split is that "he wants her for himself."
A source also says that Heidi just returned from New York City and that none other than Cougar Zank accompanied the plastic princess on the trip.
"They are definitely friends. I don't know if there is anything more to it than that, but Spencer believes there is," the source said. "He's certain."
It's reciprocal, too. One of Heidi's major concerns, close sources reveal, is that Spencer has been seeing another woman since their split in May.
"She is anxious to find out if her suspicions and the rumors are true. It is really important to Heidi to find out if Spencer has been cheating on her."
