Meg and G were all over each other ... hugging and snuggling as he planted kisses all over her face. Unclear exactly where they were at the time of hook-up, but they were sprawled out on a couch with other people around at a party.

G-Eazy posted the selfie vid, because ... who wouldn't??!! We don't know if they're a legit couple or just a weekend one-off but sure seems like he wants it to be official. He posted a pic of her -- in the same outfit from their video -- and slapped 4 hearts on it.

TBH ... Meg was, arguably, paying more attention to the lens than G-Eazy in the video. So, if they're the real deal, she's gonna make him work for it. Deservedly so!

We're guessing Halsey won't be sending any congrats to her ex-BF. Looks like he found his new bae one day after Halsey -- who was also in MIA -- went off on a guy who heckled her by yelling G-Eazy's name.