5:18 PM PT -- Khloe has followed suit, deleting all recent photos of Tristan on her Instagram.

Kim Kardashian feels betrayed by Tristan Thompson and Kylie's best friend, Jordyn Woods ... so now, they're dead to her on Instagram.

Kim pulled the plug -- unfollowing the 2 on Instagram -- in the wake of TMZ's story that Khloe split with Tristan after he hooked up with Jordyn over the weekend at an L.A. house party.

As we reported, Khloe broke up with Tristan over the latest cheating scandal, and this one has a twist with a ripple effect through the entire Kardashian fam.

The big question now ... what's Kylie gonna do? We're told at first she didn't believe the story, but after talking with friends she's come around. As you know, Kylie and Jordyn have been inseparable ... Jordyn even lives in Kylie's guesthouse.

Kim has 127 million followers on Insta and now only follows 120 folks.