Kourtney Kardashian -- Blindsided by Scott Disick Pics with Other Woman

Kourtney Kardashian and Scott Disick had their issues -- Scott's partying and substance abuse -- but seeing photos of him with another woman caught her totally by surprise ... TMZ has learned.

According to our sources ... Kourtney had long ago agreed to stick with Scott and work with him as he battled substance abuse problems -- mostly for the sake of their kids.

But we're told infidelity was never an issue between them ... so she was floored by the pics of Scott getting touchy-feely with celebrity stylist Chloe Bartoli in Monte Carlo.

We're told Kourtney also fears Chloe isn't the only girl Scott has cozied up with lately.

As TMZ first reported, Kourtney ended things with Scott after the Monte Carlo incident ... and he hasn't been to their family home in Calabasas in over a month.