I don’t understand how people can think that Dennis holds the power over Dee in their relationship.  Yes, he manipulates and abuses her, and she is forever striving to gain his approval.  However, it’s made clear numerous times in the show that Dennis actually does not hold that much influence over her.  When she thinks she’s going to become famous, Dee all too eagerly rejects Dennis to board a flight to LA, appearing perfectly fine with separating from him.  Dennis, on the other hand, loses his shit at the prospect of her leaving him.  

If anything, Dee is the one person who can influence Dennis and get under his skin.  Just by remarking that his face looks fat, she can push him into starving himself.  He exhibits intense emotional reliance upon her, clinging to her when scared or upset and always running back to her when he experiences problems with one of his other friends. It’s telling that when Dennis “breaks up” with Mac in Mac and Dennis Break Up, he goes straight to Dee’s apartment to seek solace.  In the Gang’s book, Dee mentions him crying to her countless times over his high school girlfriend Maureen Ponderosa.  He’s confessed to loving her twice and shown distress at her rebuffing him.  While Dennis and Dee both need each other, it’s evident in my opinion that Dennis needs Dee far more than she needs him.