May be coming to an end marriage?

Hey guys, do you remember when it was my wedding? I thought I was happy. Not yet passed away a month and I wish I would be single. I contemplate that I want to divorce. What is the cause of this? I accidentally met last week with an ex-girlfriend. Still I could not forget her. She just said I would like to congratulate to you. But when she said these words, hung his head and wasn't happy. And I not. Guys, what can I do? She was my first love. I'm totally clueless. Previously I wanted to marry with her. But it didn't work out. Now I'm married but not happy. I'm not in love with my wife. Missing the single life. ///_///