Although some fans are still in deep denial about Wes' death, the fact of the matter is he's really dead and gone. The only question that still remains is who killed him. The list of suspects is long and includes his father's family, any of the other Keating Five, Frank, Bonnie, and really just about any one. However, it always seems to be the quiet ones that are really guilty and Oliver doesn't seem to have much to say these days. So did Oliver kill Wes on How to Get Away with Murder? On this show, everyone is guilty until proven innocent.
At first I was skeptical about Oliver being a suspect, but then Reddit user londonbrazil convinced me. During the winter finale, Connor practically confessed to Oliver that he and the rest of the Keating Five killed Sam, which led Oliver to do some research. While he was investigating Connor's cryptic semi-confession, Annalise stopped by and asked him to hack the DA. Londonbrazil theorizes that when Oliver hacked the DA he found out why they had Wes in for questioning and that Wes was going to confess about the killings of Rebecca and Sam, putting Connor in danger of going to jail.
In the latest few episodes, fans have seen that Oliver doesn't want Connor or anyone else to go to jail, so it's possible that, in order to protect Connor, Oliver confronted Wes and ended up killing him. I can't see Oliver committing cold blooded murder, but I can see him accidentally killing Wes if they got into some kind of altercation. Kind of like how Wes killed Sam. Anyway, once Oliver realized Wes was dead, he probably ran for it, leaving Wes' body in the house and possible even setting the place on fire to hide the evidence.
It could very well be why Oliver was so stressed when he called Connor. Maybe he felt guilty because he started the fire, but didn't expect Connor or anyone else to be inside the house when it went up in flames. Or maybe he is completely innocent and was just worried about his ex who he's clearly still in love with. Fans will just have to keep watching How to Get Away with Murder to find out the truth. But until we can place Oliver's whereabouts during the time of Wes' death, I say we keep an eye on him for more possible clues to his guilt.