Love Island USA's Kendall Washington and Nicole Jacky Are Officially Dunzo

"Love Island USA" stars Kendall Washington and Nicole Jacky are officially over -- just one day after their fiery reunion showed how much they were clashing post-villa!

Nicole spilled the tea on her IG Stories Tuesday ... saying it was Kendall who hit her up that day and pulled the trigger on their breakup -- adding she's trying to wrap her head around it and respect his decision, but it's been a tough pill to swallow.

Kendall, on his end, posted he and Nicole had reached a point where it just wasn't healthy to keep going ... and asked for haters to back off and give them space to focus on their mental health.

So, what went south after they snagged 4th place on the show's S6 finale last month? Well, ICYDK ... NSFW footage of Kendall hit the internet while he was filming the show this summer ... which he claimed came from someone from his past.

But here's the kicker -- Kendall lied about when the video was taken -- and who it was sent to -- leading to lots of tension at the reunion.