Have him checked out by a vet. There's a whole slew of problems that can occur. It sounds though that he just needs some food.
Make sure his temps and environment are as least stressful as possible as well.
I won't yell since I don't know the situation.
But I might suggest that if you realize your getting neglectful to the point where your animals are going to suffer because of it, offer them up for adoption.
I think RESPONSIBLE pet ownership means providing for them at ALL times, and doing what's best for them, even if that means adopting them out to a more suitable home.