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The Weeknd & Drake Bday Partying in Vegas ... One of 'Em Hooks Up!!!

The Weeknd had himself quite a weekend -- not only hooking up with a new flame in Simi Khadra ... but linking with an old pal in Drake, who was there for the good time.

Drizzy just posted some photos that showed him having a ball with Abel in Vegas during the latter's 32nd birthday celebration at Delilah. The shots feature Drake and Weeknd embracing in the DJ booth ... and generally enjoying themselves in the lounge and surrounding casinos.

The caption he included ... "We’ve done everything like it’s nothing…isn’t that something." If you aren't familiar, Drake and Weeknd are close buds and longtime collaborators.

Like we told you, Champagne Papi was far from the only celeb in attendance -- Swedish House Mafia was also on hand, as was Kaytranada.

TMZ.com

More importantly ... Simi Khadra from twin duo Simi Haze was nearby ... and locking lips with the birthday boy, as seen in exclusive video we obtained.

There have been rumors they're seeing each other, and the clip seems to confirm they're more than just friends.

Oddly enough, Simi was also once close with his ex, Bella Hadid. Small world!!!

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