I don't think you need to be diagnosed. Most likely you just haven't met your love yet. It happens that someone falls in love for the first time at 16 and someone at 40. There is no norm when this should happen.
Probably your time has not come yet.
if this worries you very much and you want more detailed answers, then consult a psychologist. That should help you.
But first of all, stop thinking that something is wrong with you. Everyone has a different destiny.