Selena Gomez Kisses Boyfriend Benny Blanco In New Instagram Photo

Selena Gomez is all in with Benny Blanco ... because they clearly can't keep their lips off each other!

SG posted some pics showcasing some of her "favorite moments" in New York this week -- starting with a photo celebrating her pal Taylor Swift's birthday.

And then there's the kiss ... celebrating her love for Benny as she plants a big one on his lips

As you know, Selena's been putting BB on her socials, defending her relationship with Benny after some of her wonky fans blasted her for "dating down" ... referencing her prior relationships with guys like Justin Bieber and Nick Jonas.

Selena's fired back, saying she'll never date "a f***boy ever again," and that he's been treating her "better than any human being."

Good on her ... only thing is, don't give those jerks oxygen.