I keep imagining sex with a woman when I shouldn’t!!

I am married. I love my husband with every bone in my body... we’ve been married for three years and we have a child together. But! Every single time that I’m having sex with my husband, I always have to imagine me having sex with a woman for me to enjoy the sex with my husband. I have never cheated on my husband and I have never fancied a woman so I’m not sure what the hell is going on. This isn’t something I can discuss with my husband because he wouldn’t take it well, I know him. I’ve tried to get rid of the thoughts but they just keep coming back