Is it normal that i want to have sex with the same sex?

So I've been with the same man for the past two years. Lately, all I can think about is being with another women. If I'm not thinking it, I'm dreaming it. I've "dated" a women before a couple years ago, but the only thing I would do with her was make out with her. Now I find myself constantly thinking about being with another woman. The thought of being with another woman is the best turn on for me, and sometimes when I am having sex with my partner, I picture him/think of him as a women, and I am completely aroused. Is this normal? Should I put my thoughts into action?