history: I was supposed to go into work on my day off. I ended up getting sick and had to tell my boss I wouldn't be able to help. I couldn't look him in the eye for a week. 
current: I promised my boss I would go into work on my day off to assist with a project. I didn't go in and I can't look him in the eye. 
next: You should at least clear the air with him so that you dont have hard feelings