Bob (spoiler)
That was heartbreaking, though no surprise since it's obvious Joyce and Hopper are into each other. It was so sad because you could tell Joyce wasn't too sure how she felt about Bob at first but knew he was a great guy who accepted her as a single Mom and her boys, but at the end she seemed to have fallen for him after how he stepped up after learning the crazy truth about what was going on with her and Will.
RIP Bob :(