How to quit job?

I've been working since I was 17 weeks pregnant. After my son was born, I started taking him with me to work. He's 9 months old now and honestly, I really want to be a SAHM until he starts school.

But my boss is such a nice man that I feel awful about possibly quitting.

My husband is supportive of my idea. We don't need the extra cash like we did. Our apartment is income based and once my husband goes into management at his job, I'd have to leave mine anyway or whenever I do my recert papers next year, we won't qualify because we would make too much money. I just don't know how to go about telling my boss.