Wes' character development is one that can only be described as depressingly unfortunate. He's introduced to us in Season 1 as an eager, naive, bright and insecure college student, trying to manage being in college and working for Annalise. Sadly, it doesn't take long for this to start spiraling out of control. He somehow ends up killing Sam, Annalise's husband, to protect Rebecca, his then girlfriend.
As a result, Wes, Michaela, Connor, Laurel, Frank, Bonnie, and Annalise must figure out how to cover up this murder and throw the police off their scent. By the end of the season, Wes is a completely different person.
Mourning his girlfriend
Season 2 begins with Wes under the impression that Rebecca, his maybe-sorta-ex-girlfriend, is alive and in hiding. The audience knows that Rebecca was actually killed, and we later find out that it was Bonnie who suffocated her to death. Rebecca's disappearance sends Wes into a deep depression and causes him to distance himself from the rest of the Keating 5.
He grows suspicious of Annalise (rightfully so) and convinced that she knows what really happened to Rebecca. Eventually, Wes finds out that Annalise knew that Rebecca was dead and lied to him about it for weeks. He responds by shooting her in the stomach.
Hating Annalise
Wes remains distant from everyone even after he shoots and nearly kills Annalise. Besides Laurel, Wes spends hardly any time with anyone. After Annalise returns home, Wes seems desperate to see her but not remorseful at all. Wes feels betrayed and manipulated by Annalise and their relationship continues to worsen as he tries to get more information from her. It is later revealed that not only did Annalise know about Rebecca, but she also knows about Wes' mother, father, and what happened to him as a child.
Wes' parents
As a child, Wes lived in poverty and had to deal with mother's mental illness. Although he was told that she committed suicide, he continues to wonder if there's more to the story. He learns that his mother killed herself due to the stress of a court trial that Annalise needed her to testify for. He also finds out that his father is Wallace Mahoney, a wealthy businessman that raped his mother. Wes' lack of knowledge about his parents plays a huge part in his emotional unavailability and lack of trust.