Character Analysis
Pick one word to describe Dennis. Ready? Go. If you picked solid, well, you might be Meg Wolitzer. Dennis is "regular," as Isadora calls him, but we don't really find out how much until later in the book. This is one down-to-earth, no-pretense kind of guy. He plays football on the weekends and is completely comfortable living in a tiny apartment with Jules; he also ends up being a great dad and, briefly, a great camp director.
The main thing we learn about Dennis is that he has seriously struggled with depression, and is wholly dependent on his medications for his current stability. When those fail, he spirals into a lasting depression that threatens his marriage, and that no one really understands. He ends up getting a new drug that works wonders for him (yay, science), but the depression's always there in the background threatening to come up again.
Dennis is a paradox, a burly guy with really vulnerable emotions. Or, as Jules says, "There was no life Dennis burned to live except, it seemed, a life that wasn't depressed" (4.154). In this, he provides an important contrast to Jules: While she yearns for frivolous things, Dennis steadfastly just wants to find a way to keep his head above water and enjoy being alive.
That being said, Dennis makes up for a lot of Jules's failings just by being himself. They're pretty opposite personalities, so Dennis is the one that puts checks on Jules's self-pity and envy of her friends—and while he doesn't have infinite patience, he definitely supports her through a lot of her bitter moments. Plus, the possibility of losing this big bear of a guy is the first time Jules really appreciates what she has instead of whining about her friends' successes. Dennis is the character it isn't hard to like, which in this book, kind of makes him a standout.