The notion a romance and love being the core of relationships and marriage is relatively new. Such unions used to be primarily economic and strategic in nature. You had better odds at life if you had a family. Sounds weird since it means more mouths to feed, but together you could do much more that one person could - division of labor and extra helping hands.
In recent years however, with the advancement of technology we are less reliant on physical labor and can manage households a with less effort. Add to that influence from media and literature and the emphasis has switched from practical reasons to romantic reasons. While our brains have always been wired to us being social beings and needing a "tribe" the biological reasons for this need have diminished. Add to that decades of influence from romanticism and we find ourselves craving love, relationships and companionship with the level of heightened emotions we're used to seeing in our daily media. But life isn't all heights. Life isn't endless bliss where we get to "live happily ever after".
While your question focused on the sexual nature of relationships, it can not be answered ignoring all the other factors coming at play. From my own experience I've seen people craving relationship while not knowing what it is, what it entails and feeling let down when it fails to match their expectations. The result - countless new attempts that end the same.
I might be leaning more towards an area that is more closer to myself in this subject and that is the definition of love. What it means to love. How does a person fall in love. And is it possible to feel close to someone but never fall in love... Because as I said before - our perception of love and relationships is constantly shaped by our environment and society. Ridding one self of those influences you start to ask yourself what do these things actually mean to you.
I used to ask the same question as you. That was back in the 2010's. When I wanted to find a partner for life, while it seemed that everyone else was interested only in sex. There had been exceptions.. that never played out due to several reasons, mainly geographical. Fast forward to today, with all the scars both on my soul and body and I have learned a lot, but I find myself having even more questions than before.
I can see now how I used to come on too strong. Like I felt that I desperately needed to get into a relationship. Got a hard lesson of how my world view was twisted into thinking that I do not matter and that the person I would love matters above all, so I'd sacrifice everything for him. I remember from my childhood that we were told stories about love, how we've been sent to this world as halves destined to find our match and become whole. Subconsciously that mindset rooted in me. Not from that one tale, no. But from the collection of every peace of information about love I was exposed to. As a result I always felt incomplete and felt like I needed to fill a void.
I fell in love really hard. Got hurt even harder. But it opened my eyes in many ways. Nothing gets you out of depression better than cutting out a toxic person that's poisoning you slowly. Met people, gained experiences. Started to see life differently. Started to put my own needs first, like my mental and physical health, took risk changing job. And started to re-asses my mindset.
And right about that time I also met my current boyfriend. Ironic, isn't it. But as I said before - life isn't a fairy-tale. There are ups and downs and there have been arguments and we've been close to breaking up as well. Life is ever changing and we need to be okay with that.
I used to get mad at guys who answered that they're not looking or anything particular, just looking at what's up. But after all this time I think that they are the one's doing the right thing. You can't force things. You can't force love, it should just happen.
Sorry for the long rant. Hope you can find at least something that helps you.