Well I think the movie was released in 2009.. but I am not sure. It is about a couple who lives in a city and happily married. The wife is energetic and wild and her husband is slow and little dull. Wife went to some different city for some work where she finds her husband in completely changed attire and looks. She thinks that he is her husband and he is giving surprise to her. But actually this guy was a look alike of her husband, not his husband in real. She enjoyed with him and had many sex scenes with this strange guy. But later she found that this guy is not her husband so she started to avoid him realizing that he is a look alike of her hubby. The stranger start to behave as a psycho... and finally at the end her real husband kills that guy.

Please help me finding out the name of that movie...

Impulse (http://www.imdb.com/title/tt1078899/)