Once someone makes their marriage vows they in a way sign away the possibility to be in other open relationships. Marriage is more then sexual satisfaction. It is also human for you to miss sexual intimacy.
You may want to ask your question how you would feel if you were in your husband's shoes. As far as whether it is wrong to have a lover or not would depend on your moral and spiritual belief system. A sexual act takes a few minutes but true love takes longer than that. Soul searching is needed to figure out what is that you really want out of your current marriage and out of life especially for your self. What you feel is human and what you do as a result of it would be something that you will have to decide and come to terms with.