Single life can indeed be rewarding and fulfilling, I can attest to that. But I experience residual feelings of longing for the intimacy and commitment that a partnered relationship can provide.

I hear what you say about investing in friendships, but I find that in our culture, most people don't value friendship very highly, particularly when they have a committed primary relationship or marriage.

I'm a singleton by default, because after literally decades of looking for an ideal partner, and finding the whole process frustrating and futile, I gave up and started to celebrate my single life. It has many advantages, like freedom to do what I like when I like, but there is still a part of me that feels something is missing.

Another issue is often feeling weird about being single in a world that is largely coupled up. I live in Spain at the moment and hand-holding couples are everywhere. I go into restaurants and cafeterías by myself and feel really weird. I see couples old and young all around me. This feeling of being odd follows me everywhere I go. If I were in a romantic relationship, I think those feelings of strangeness would dissipate and I would feel like I fit in.