I want monogamy, but not as it is popularly

I don't want a relationship with someone who has decided to be monogamous, but rather someone who is naturally that way. How unusual is it to find a person like this?

I'm demisexual, and I confess that I don't like the way people treat monogamy these days. Relationships where people fantasize sexually about other people, consume pornography or soft porn, desire others and so on. I know this is considered "normal" but for me it isn't, and I wanted to have a relationship with someone who also thought like me and was naturally like that.

It's not even a question of insecurity, but I think it's a bit like only wanting one person, and having them fantasize about several others.