It must have taken place in some alternate dimension for that girl to date the loser character that was so prominently on display. When I saw the photo of her on his desk, I assumed Daniel Baldwin would rip on him for leaving the model photo in the frame. The movie never addressed this glaring mismatch, causing several reviews that touch on the topic.
The film would have played out a whole lot better if he didn't have a girlfriend at all. Also, roid rage is a myth, do some research before making a full length feature.
As for the ending, I didn't understand it. Was he big the whole time? Did he actually get big but had dysmorphia so he wanted to get even bigger? There seemed to be some sort of revelation by the main character but I couldn't figure out what it was.