Sex and relationships are two different things.
Sex can be a casual interaction between friends, for example. I had a good friend that I used to hang around with a lot. We had no intention of being in a relationship, and no desire to do so. But we had sex pretty much every time I was over. Casual sex is fleeting. Fun, and can definitely be emotionally fulfilling for a time, but ultimately it’s a passing high.
A relationship is a deeper. If you’re wanting fulfillment that can’t be satisfied by sex, you’ll need to actually get with someone. You can do chain monogamy if you’re not wanting attachments, or go whole hog into a relationship.