I have worked my entire marriage. My husband worked for 5 years, but then quit his job to be a stay at home dad. If we get divorced will I be forced to pay him alimony? We have been married 9 years and have one child. I would want full custody.

First don't expect to get full custody, as the stay at home parent, he may have a good chance at it, or at the very least joint custody. Next yes of course you may have to pay it, it has nothing to do with male or female, it has to do with one partner being the main supporter of the family and paying to help the other till they can adjust.

So seriously, think joint custody and you paying alimony.
Also depending on the state, if you have joint custody you may still have to pay child support if you earn more than the other partner

Being married 9 years and he stayed home for 4 out of those 9 years really does not look like he'll be collecting alimony. Depending on what state you are in that time frame would not mean he gets alimony. Alimony is only granted when the (for instance) woman stayed home for 15 or 20 years and did not pursue any career or have any specific job training or education. Since your husband voluntarily quit his job to be a stay at home "mom" he can easily go back into the work force and get a job. Alimony is granted so the woman who stayed home can get an education to then enable her to join the workforce and get a job so she can support herself and her children. It is only granted for a specific amount of time anyway usually only a few years at best until the woman completes some sort of schooling or training. It's not just a "handout" that keeps on indefinitely either. This is, of course, dependent on what state you are in.