Billie Eilish Kisses YouTuber Quenlin Blackwell at Coachella

Billie Eilish is leaning into the fact that she's into girls -- planting a kiss on a female YouTuber at Coachella ... and smacking the gal's ass while she's at it.

The singer was filmed at the music fest this weekend, where she smooched with Quenlin Blackwell -- a Gen Z content creator who's been hanging out with BE a lot lately ... and with whom she's sparking romance rumors after this PDA moment.

Watch ... Billie could be seen grabbing Quenlin's face and pulling her in for a kiss while enjoying music at the festival. It wasn't super show-y or anything ... still, a kiss is a kiss.

Not just that ... but Billie was also filmed dancing with Quenlin at one point, grinding up on her and giving her a few good spanks while music was blasting, with both of them onstage.

Billie and Quenlin have been friends for some time ... with Billie often appearing in QB's TikTok videos alongside actress Odessa A'zion. They're always goofing around and are very comfortable around each other ... so, it's unclear how serious this really is.

What also makes this interesting is that Billie just dropped a new song at Coachella ... it's called "Lunch" and it's all about her having feelings for a woman. As we know, Billie came out last year and revealed she was into ladies ... although, the announcement was wonky.

Either way ... Billie's obviously not hiding that anymore, going in for the kill with QB. Whether it turns into anything else more serious ... we'll see. Billie's only publicly dated dudes.

Billie's third studio album, "Hit Me Hard And Soft," is set to drop in May -- and folks are anticipating some bombshell lyrics.

If her girl-on-girl actions here are any indication ... get ready for more of that.