Will has been a fan of the Orioles, Senators, and now Nats, and yes, the Cubs are a guilty pleasure, however, he is a (or has been) a minority owner/director of the Orioles and Padres. To say he is exclusively a "Cubs fan" is a bridge too far.
All the more reason to hate the Cubs.
The Cubs are Will’s favorite team, by far. Fact. Had it been Cubs vs. Nats, he’d have laughed if you asked who he’d be rooting for. Thought everyone who knew baseball knew that. Guess not.