Husband involved in a haraam relationship

I need some advice on my marriage problem. After four months of my marriage my husband confessed to me that he doesn't love me at all and is in love with another girl from before marriage. He only got married to me because he was angry and wanted to get over her. He never gave any feeling like he doesn't like me at the beginning of marriage he even accepted me as a wife, it after 2 or 3 weeks I could see he was changing and had a strong gut feeling. Now he asking me for some time to change but doesn't know exactly how long it will take. He accepted he loves his ex too much he doesn't know if he could forget her and start loving me. I really wanted to know in this situation what am I supposed to be doing, are we still supposed to be staying together as wife and husband and is our marriage still valid can I also include all this is really affecting me mentally.