Marco came in with his heart on his sleeve and a guitar strapped to his back — and he completely won us over. He devotes his time to helping Elle with the Dance Dance Revolution competition, and though his motives aren't completely altruistic (he's obviously into Elle as more than a friend), he doesn't push his affections on her in any way. He doesn't hide his attraction to Elle, but he lets her make all the moves — and is understandably crushed when she runs away from him after she kisses him.
The end of The Kissing Booth 2 sees Elle going back to Noah after her moment with Marco, but the way he stares after her alludes to things not being quite over between the two of them. I don't necessarily believe that Elle deserves another chance with Marco since she broke his heart, but I wouldn't be opposed to seeing how the two of them find their way back to each other in the third movie.