how can i apply for the citizenship?

I came in March of 2005 with a visa as somebody's employee I got married on August 2005 with a guy that had a work permit, but he was doing his paper to get the green card, so he got my papers into his case we both got the green card on April of 2007, things didn't work out between us, so we are not together and we didn't have kids. I've tried to apply for the citizenship but they are asking me for his information and i don't have it. What can i do? Should i get divorced first?