The source says that the Hills starlet is currently staying at the Malibu home of Cougar Zank, a mutual friend of Heidi's and Spencer's. He's a former Marine who soon became a bodyguard and a small-time actor. He is currently working on a script with Pratt.

Since the split, though, he's invited Heidi Montag over to the house he rents. Spencer Pratt was appalled upon hearing the news, considering Zank his friend and not his wife's. His jealousy sparked up and he accused the man of wanting "[Heidi] for himself," an insider divulged.

But while Spencer hasn't acted on his suspicions, aside from yet another whiny tantrum, Heidi Montag is busy with hers. She believes that her husband has been seeing another woman since she moved out.

"She is very anxious to find out if her suspicions and the rumors are true, especially if he's spent any money on another woman," the source said. That's why she enlisted the services of a detective to tail Spencer Pratt.

"Heidi has hired a former member of the sheriff department, who now works as a private investigator, to look into it. It is really important to Heidi to find out if Spencer has been cheating on her."

Well, perhaps she should look into the possibility that none of this is really happening and they're just creating their own problems. Even MTV News is pondering the reality behind this Hills controversy.

Heidi Montag Sorts Out Legal Separation from Spencer

Besides, there are many more complications here. Spencer and Heidi have indeed split up, so would an affair be illegal? A more pressing question, however, is this: why would Heidi reveal that she's secretly spying on Spencer?

(Image Courtesy of WENN)