SO FRUSTRATED

Why does he have to be so damn frustrating! I can't have one freaken day of being in a bad mood? When he is in a bad mood I try to make him feel better and be encouraging and take extra caution to not say anything that will hurt his feelings. Today I don't feel good, I got no sleep and it's just a bad day but no instead of him being helpful or encouraging he gets pissed off that I'm in a bad mood and acts like an ass to me. Why is he allowed to have bad days with someone there to try to help him through it (me) but I'm not allowed too???