Alex was the subject of one of Hannah's 13 tapes. Her one-time best friend, Alex "ditched" Hannah when he started dating their mutual BFF Jessica (Alisha Boe). When his relationship with Jessica soured, he made a "hot or not" list and put Hannah (Katherine Langford) as "best ass" and Jessica as "worst" — which led to the end of Hannah's friendship with Jessica and to bullying and groping from gross Liberty High boys.
Yet Alex also takes Hannah's death incredible hard. At the end of season 1, a depressed Alex shot himself in the head. At the time, fans were completely in the dark about whether the musician would return to see another season, or if he would meet the same fate as Hannah (Katherine Langford) did before the events of the show.
Fortunately, Alex survived his self-inflicted wound. As fans learn early into the sophomore season, the bullet went through his skull but ultimately did not kill him. Though we don't see it during season 2, Alex was apparently in a coma for some time, and when he woke up, learned that he had some impairments that could be worked through with physical therapy.
The Alex we know in season 2 walks with a cane and exhausts easily — his body is simply not as physically strong as it was in the previous season, which we can assume is from the traumatic brain injury he suffered.
However, the issue that really disturbs Alex is the memory loss he suffered following his trauma. Alex has lost an entire month of memories, which include listening to Hannah's tapes. Though he knows what was on his own tape, he can't understand why he would choose to end his own life because of what Hannah said.
At the time, many fans couldn't make sense of it, either: While Alex played a role in Hannah's bullying, he should hardly bear the same guilt as, say, someone like her rapist Bryce (Justin Prentice).
By the end of the season, Alex remembers what caused such tremendous guilt as the final pieces of Hannah's story are put into place. With a new hair 'do (goodbye, bleached-blonde locks) and fresh perspective on life, Alex is finally ready to begin not just the physical healing process, but the emotional one as well.