Loneliness is one of the worst things that can happen to a Human being. It is a terrible and horrible feeling. Being alone for too long can cause a person to become bitter, sad, depressed, pessimistic, edgy, and uncaring among other things as well. It is not good to be alone for too long Mark. You can be by yourself at times if you want, some people like to be alone sometimes, however everyone still needs some form of love, for love is the most important thing a human needs. Whether that be love from a friend, family member, or a romantic lover, we all need a bit of love in our lives.
From a scientific standpoint though, since you seem like a science man, humans are social creatures. Without any form of human interaction for too long a person can go depressed to point of suicide, or even insane.
I understand you have had bad experience with people in the past, but that does not mean all people are bad Mark. You may say all the people you thought cared for you actually never did, but perhaps you only wish to believe that because it rectifies all those bad experiences. Perhaps you wish to believe all that because it rectifies your belief that all humans are evil and that there is not true love. But maybe you are wrong Mark. Maybe some of those people truly do care for you, maybe there is such thing as true love and friendship... and you are just in denial.