Is this okay???

So I'm bisexual but have been with my fiancee (male) for 6 years now and have never been with a woman. Recently I've been stuck thinking about what it would be like to be with a woman sexually and just dating one. It makes me feel guilty because I'm not sure if I should be feeling this way or what it means. I need some insight from those who may understand what I'm going through. Please help!