KOURTNEY KARDASHIAN and Scott Disick are fighting over another man – Scott’s new BFF!

The 33-year-old reality star is furious that Scott – the father of her two small children – has fallen into a blossoming “bromance” with professional race car driver and Miami Beach businessman Chapman Ducote.

“Since the moment they met, Scott was instantly taken with Chapman,” said a source. “They dress alike, they have the same hair, and all they do is constantly look at each other…it’s like they’re looking in a mirror!

“Scott is practically drooling all over Chapman.”

According to the source, not only is Scott, 29, dressing like Chapman, he’s taking race car driving lessons from him!

But what’s really rubbing Kourtney the wrong way is the fact that Chapman has been urging Scott to get married, which Kourtney has made clear she’s in no rush to do.

“Chapman is married to a beautiful attorney, and he constantly tells Scott the importance of being married,” explained the source. “So Scott goes home and harangues Kourtney about getting hitched and they end up in another argument.

“That’s one reason Kourtney is so upset about the friendship.”

Ducote, 36, is scheduled to appear in several episodes of the new season of “Kourtney & Kim Take Miami,” which premiered on Jan. 20.

At this point, Kourtney is so fed up with the new friendship she’s given Scott an ultimatum.

“Kourtney told Scott that if he continues to listen to Chapman instead of her, their relationship will be over,” noted the source. “But Scott doesn’t seem to care. She’s given him ultimatums before. As far as he’s concerned, Chapman is his big pal and there’s nothing Kourtney can do or say about it.”