I will only have sex with one man

I have been with my man since I was 18, I lost my virginity with him a few years ago. We are now engaged and I love him with all my heart. He is the perfect person for me and we are very happy together. We also have a good sex life but I don't know why I started to wonder how would it be to have sex with someone else. I will spend the rest of my life being loyal to him so I will only have sex with one man in my entire life.

Am I bad for feeling this way? Have you ever experienced something similar? Please help!