This is cliche but you probably just haven't been with the right person You may have missed that instant spark but still continued with the relationship, or the relationship ended before your feelings could develop for the person. There could be other external and internal factors, maybe the timing was wrong, are you happy enough with yourself and your life to share it with someone else?
from your words I sense a longing to actually experience love, I don't think someone who is incapable of love would say that.
There is a noted psychological phenomena where an individual is incapable of love through extremely traumatic past experiences. Did a paper on it a few years back... Anyways. It may be that you've just dated folk with different keys to your emotional lock. Or you could just not be the overtly warm and fuzzy type. You can be with someone and it's not much more than that...Or! You could just take a super long time to fall in love. Whatever it turns out to be I genuinely hope you find happiness in life :3
Just because you have lustful feelings doesn't mean that you're made for marriage.
The mind is an important part of love. So is the heart. Mere lust is not necessarily an indication of real sexuality. It just means that your body is sexual. It may be that you're made for a different kind of love.
a sexual relationship is not the only place where one encounters love in this life, believe me. The more intense forms of love are not exclusive to such a relationship.
"If you're ACTUALLY sad about being single, don't go posting it on the internet for everyone to see. It's NOT gonna work. and if you're in your teen years and younger, i know a boyfriend or a girlfriend might seem like the most important thing in the world right now, but TRUST me, it's not. I'M 21. I'VE BEEN A TEENAGER FOR LIKE 10 YEARS. I KNOW. so STOP worrying about being alone! Just smile and live life to its fullest! There's ALOT more fish in the sea! AND REMEMBER! The world... is your oyster. and one day you're gonna find your pearl. ...Or unless your oyster has no pearl... then in that case you have to get another oyster which means you have to get another world... Yeah, It's not looking good for you." -Nigahiga
Some fall in love very easy and some it takes a lot before they truly fall, you might be in the second category here. Maybe write down on a piece of paper what kind of person you'd like to grow old with - everything you come to mind like blue eyes, tall, kind, rich, likes DnD and so on... and don't think about the ones you've dated before when doing this - take your time and just brainstorm and then edit away after that. I think you will come to some clarity through that.
Now, I don't know your sexual orientation but maybe you're looking at the wrong gender? That's also an explanation. Idk.
I know though that sooner or later you will fall in love, most people do that - if they're not psychopath or sociopath of course. If you think you might be then go see a counsellor and say you need some investigation.
It can also be so that you haven't let your guard down or that you're not ready to love someone. There are lots of reasons to why a person can't love.