If I'm married with a US citizen since 2012 and I have green card, can I still apply for citizenship if I divorce him?

Generally, the divorce of a foreign national who has been Permanent Resident for at least four years and nine months should not interfere with her eligibility to apply to become a naturalized U.S. citizen. In the naturalization application process, it would be feasible for the USCIS adjudicating officer to inquire about a divorce in order to determine whether there may be reason to suspect fraud in the foreign national's adjustment of status, but where a marriage has lasted five years, that is unlikely to be a serious concern. Of course, there are many other details that determine eligibility for naturalization, and any special circumstances relating to the divorce could require additional attention. It would be wise for you to consult with an immigration attorney who, after learning all of the relevant information, could advise about eligibilities, options and strategies to attain your goals, and who then could offer legal representation in the often complex application process.