How do you think of sex?

My husband and I recently had a conversation about open relationships and sex and he revealed to me that maybe later in life after we've been married and only sleeping with each other for a long time, an open relationship could be beneficial because to him "sex is just sex" and gets boring with the same person. Not gonna lie, I was floored. My initial thought was why the hell didnt he tell me this before I married him? Marriage means alot to me and I've never ever considered anything outside of monotony. But I'm an understanding and open minded person, so I heard him out and it got me thinking of how others perceive sex. I have always thought sex was better if you are passionate about someone, when you are in love and 100% comfortable with this person, your person. He says sex is just sex - purely for pleasure with someone you are simply attracted to. Is this a male/female difference or person to person? Let's hear your thoughts!