Annie, you are dead on it Most states do have separation but some states like New York you still have to provide support which means that you really can't afford to live on your own unless you're living with someone else already. New York still actually has grounds for divorce one of which is living apart for a year or more. Again every state is so different that you really need to talk to someone that has expertise in the state you live in. I hear Massachusetts is an absolute nightmare.Many states also have a thing called "separation". You are not exactly abandoning your spouse, but it is not a formal divorce either. It might lead to somewhat different financial results. Or not. A divorce attorney should know specifics for their particular state.
(My state doesn't need any grounds for divorce at all, so here it wouldn't matter.)