Either Heidi Montag and Spencer Pratt are honing their acting chops through their contrived separation, or the "dueling" duo really have hit a rough patch. Regardless of what the case may be, Radaronline.com is taking the bait and reporting that feud between the Hills has-beens has escalated to the next level as they accuse each other of adultery. In fact, Montag is supposedly so sure that her estranged hubby is having an affair that she's gone so far as to hire a private investigator. In what's surely made-for-TV-drama, Montag insists that Pratt has been seeing another woman since their "split" last month. An insider tells Radar, "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. 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." And Montag isn't alone in her suspicions. Pratt's radar has been on high alert since Montag moved out of their Pacific Palisades pad and shacked up with Pratt's pal "Zank," a wannabe actor/bodyguard. The source says, "They are definitely friends, and I don't know if there is anything more to it than that, but Spencer believes there is. He's certain there is." She's currently staying in his posh Malibu pad. Zank also tagged along with Montag recently when she was in New York to pitch a new reality show with her and pal Jennifer Bunney about two single ladies traveling the world. Of course, the timing of the split is suspect because Montag would only be able to film such a show if she's not with crazypants Pratt. While many continue to speculate the split is anything but real, insiders maintain Montag is very concerned with the bottom line. Says a source, "Heidi is very concerned about the finances. Everybody knows she's made more money than Spencer. She needs to protect it." Montag filed for a legal separation last week in an effort to protect her assets... and her money, too!