*People says it has a Marc Anthony plant who gave them the scoop on what led to his sudden split with Jennifer Lopez – although it wasn’t really sudden, according to the source.

The decision to separate actually came “after months of nonstop arguing,” says the source. There were issues on a movie set, envy on the “American Idol” stage, and times that Lopez, 41, feared her husband wasn’t faithful, People reports.

An Anthony insider disputes infidelity claims and maintains the 42-year-old always supported her career. “They started to see life differently,” the source says.

As they move on to the next chapters of their lives, the Anthony insider also says the breakup is for the best. “Though they love, admire and respect each other very much, they just needed to be apart.”

More details of the split are in the magazine’s next issue, on newsstands Friday.