How do I do I file for divorce if I haven’t heard from him since September?

I have been married to a man whom I believed was the love of my life since April of 2013. About two weeks after marrying him, things began to quickly change. He was no longer attentive, he ignored my financial and emotional needs and he even went as far as to tell me he was no longer attracted to me. I was tired of the neglect, tired of going to events with family and friends and having them ask me where my husband was and saying all the time that he should come and how it is such a shame he doesn’t spend time with me. They would always ask me when we were having children. It was hurtful and embarrassing. He actually had me believing that I was crazy. In September of 2014, I told him I wanted a separation. After arguing with me, he agreed. Things continued to get worse. We moved in with my mother in September and she asked him to leave in January. I moved in to my own apartment in February 2015 and have been there for almost a full year. As in my marriage, I pay my own bills, buy my own food, and pay for my pets. He has a green card which he obtained through our marriage and I need to know what to do about getting a divorce. In September of this year, he tried to make me sleep with him, I have since told him he is not to contact me for any reason other than to discuss our divorce. I have not heard from him since. I need this divorce and I need it as soon as possible. I want to be free of him and be able to move on. What do I do?