With Social Phobia
Spidey avoids situations with many people, and has trouble keeping friends.
Since Peter was born he has felt anxious around others, and been afraid or being judged by them. After his parents died, these symptoms got worse and were harder to ignore. Since he was bullied in school and only had a couple friends, who he had trouble keeping, he would withdraw himself more and more.
Social Phobia affects about 15 million American adults
Losing his parents at such a young age left his traumatized and his fear of losing more people he loves he has trouble holding down relationships. He has been bullied and put down, so this could be why he is afraid to be judged and why he avoids others.
Psychotherapy can help teach him different ways to think and act so that he won't feel as anxious or scared around other people. This method can help Peter practice his social skills.
Medication is another form of therapy in which he could be prescribed antidepressants of some sort.