an person who doesn't have a constant need to be around other people

A loner is a label for a person who shuns human interaction for a variety of reasons. These reasons can range from a lack of certain social skills (such as people with Asperger's Syndrome), misanthropy, excessive rejection from others, or just for a desire to be with oneself. A common psychological term used to describe the personality of loners is introversion.

a person who avoids the company or assistance of others