So another preview for this one was posted. Not sure if I'm allowed to post it here or not, but just to be safe, I won't.
Seems Dewpider's a punching bag for a lot of different Pokemon at first, it finds Lana playing with Popplio on the beach, falls in love with her in that one scene where they're all underwater, we see Dewpider battling Surskit at another point and Lana speaking some words of inspiration/ganbate!! type stuff with Dewpider. It is extremely obvious she's going to catch it.
I am a little confused as to what Dewpider's moveset is, though. It seems to show two different attacks in this preview. One where it shoots bubbly foam out of its abdomen and one where it pulls bits of water off of its water bubble and throws them at Surskit. Surely it doesn't have both Bubble and Bubble Beam, that would be extremely redundant.
Unfortunately, I'm also kinda starting to think there is no jealousy with Popplio. That she's moreso just annoyed with Dewpider being clingy in that particular scene, because she doesn't seem to have any beef with Dewpider at any other point in the preview. And that makes me fear the writers won't really do much with them and do the bare minimum to set them apart ie Popplio learns Sing, Dewpider evolves and learns a Bug move, and that's basically it.