Miss Having Sex

I'm in a relationship but sometimes I really miss having sex with other people. I'm not unhappy in my relationship and we have amazing sex. More often than not I get mine. I don't know what it is with me... Instarted a new job and only one guy works there and I worked with him for the first time tonight. He's attractive and smells so good. I love the way people smell. It has a huge affect on me when they smell good. I kept fantasizing about him at work and it was driving me crazy cause it's not like I would ever do anything with him. I always fantasize a lot about my ex fwb. And just random people throughout the day I happen to find attractive. At least it crosses my mind when I see them anyway. What is wrong with me? I feel like I'm not supposed to want other people if I'm happy in my relationship. Which I am. So why do I feel this way?