I think Jackie's cute, but I'm also skeptical of their relationship due to the little bits of foreshadowing that seems to point to it being a stepping stone type of thing. In Sleepover, Marco even admits himself to the idea of him putting Jackie on a pedestal. And the broken heart on her skateboard? It just seems like they're planning to have them break up at some point, and it being major character development for Marco and Star.
I don't really care either way, I'm in this for the bug waifu. Though, I gotta say, it does alarm me how much I identify with Marco.