So, I have been giving this one a lot of thought. Will is the only one in the group who doesn't, and hasn't, had a romantic relationship. He also seems really jealous around Mike and El when they are together.
At first I thought this might be because he doesn't like being a third wheel, but now that I think about this I think that he may have a thing for Mike.
This would also explain why he lied about El commissioning the painting, because I think we all can agree that it was Will who lied, because he was trying to hide his feelings for Mike as El's because he doesn't want everyone to know.
Comment your thoughts. Is Will gay?