You know what I noticed? Every time one of the members of the kids' party is missing, they gain a new one. When Will was missing, they met Eleven, when Eleven was missing Max came along. One thing the writers did well in establishing is that each member has a role within the group. Mike is the level headed leader/ voice of reason, Will seems to be a peacemaker, etc. So, when one of them is missing it really feels like they're missing. When Will was in the Upside Down, it felt like a part of their group was gone. While I loved season 2, it was sad that the team felt so divided, even more so than season 1. Will has been missing/out of it for the entirety of both seasons, so i'm pretty sure he's never shared a scene with El (not counting the Snowball Dance because we didn't see them interact). Meanwhile, he's also barely interacted with Max, and Max has hardly interacted with El. So, that's one of the things i'm most excited to see in season 3 (hopefully), is seeing how those three interact with each other and how they fit into the group now that they're all fully settled.