1. He’d been alone his whole life because he’s autistic and quiet and awkward and had a hard time connecting with other people, so he convinced himself Being Alone Is Fine, Then. Just had utterly no hope left of ever being NOT Alone.

And then 2. after meeting Drum [another super autistic-coded character, surprise surprise] and establishing a Genuine Emotional Connection With Another Human Being for the first time, he promptly became incredibly jealous of Delta upon realizing that Drum clearly had a Much Stronger Bond with Delta. Not understanding what Human Feelings And Emotions Are, so being unable to realize that That Icky Feeling was jealousy, and not being able to fathom that a person can possibly have More Than One Friend, because the idea of just having even ONE was so foreign and decidedly unattainable to him, Gwyn thus decided that Trying To Make Friends has once again ended in failure except it is 500x worse this time because he actually cares about this person he now mistakenly believes to be rejecting him. So he started Aggressively Trying To Push Drum Away because all of the confusion caused by Liking Drum was Distressing and Overwhelming and Causing Him Immense Pain that he did not know how to express.