Well, I'm 22, and in basically the same boat. In fact, when I was 18, I would say I was in the identical boat. And I've always been this way, more or less.
So you aren't the only one.
My relationships with most people come and go. It's not that I'm anti-social or can't socialize, I just don't do the "hanging out" thing or enjoy it at all, so the new friends I make slowly disappear. The girls I get involved with are flashes in the pan because while I have a deep love for many women I've known, lifestyle choices (so far) haven't made long term relationships productive. I always feel connected to these women, and I don't mourn breakups.
I meet new people all the time, and for awhile they contribute a lot to my life, and then they pass away. This doesn't sadden me.
In truth, the closest friends I've had are internet friends who I've never met in person. It's a lot easier to find someone that fits into your lifestyle online. Some of my internet friends I've known for 7 years now, and talked to consistently about real life issues throughout those years, stuff that I rarely get to talk about in person just because most people I've met can't relate.
For many years I felt a lot of shame because society considers this kind of life to be unacceptable, but over time I've got more and more comfortable with myself and learned that social norms are not a good metric for mental health.
There's a new age take on this that, over the years, has seemed more and more true to me. The Indigo child phenomenon - people literally not born for this present earth but born for the coming earth. Born for the "new" earth of the "new" age that is right around the corner. Many "Indigos" find very little to identify with in the physical consensus reality, and by nature have their awareness pointed in another direction. Apparently, from a psychological perspective, the indigo archetype is truly unprecedented in human beings. We may very well be a new type of person for a new time.
What purpose do I find on this Earth? Very little of it interests me... the small slice of experience that does interest me is entirely centered around personal development, with the intention of being of service to the personal development of humanity. I am motivated by essentially nothing besides this... no emotional drives or physical drives, no major cravings or aversions, no major anger or hatred and not all that much stuff which could be identified as past karma. There is certainly plenty of grist for the mill - fate ensures that. But nothing of the kind that I see others deal with. In a lot of ways, my physical existence is a flatline and the entire activity of my life has been in a different realm of existence.
It's taken me years to realize that I was truly different - not just that other people are mysterious or hidden - but that I truly march to an odd drumbeat.
Some say we've come here to balance ourselves primarily and secondarily to usher in the new earth. I have no proof of this but as my awareness matures, there is a knowing from within that tells me this is truth.
Food for thought
Oh, btw, I still haven't figured out how I'm going to "live" my life. Right now I'm moving towards being a kind of counselor so I can quietly work on myself while helping out people with their issues. It's not that I'm highly motivated to this particular job, just that I recognize I need to live somehow, and also I recognize that I am completely disinterested in every activity that doesn't either improve myself or improve others. So I'm aiming for a job where I can spend the majority of time helping out people with their important issues - which is to say, help out people in dealing with their karma. Help out people in their own spiritual development.