It can't be Ash, he's a little short and also two weeks ago, he was at Mouse's when Rose was spotted by her grandmother. It can't be Johnny as he seems a little tall for the body. Dr. Sullivan, maybe, but then again that would be too obvious. I don't think it would be Greg, he doesn't strike me as the kind of guy who would be this calculated into doing something like this. It can't be Christian, he would also be too obvious as a suspect as well, and plus they would be repeating the same storyline they did with Chip by saying another love interest of Tabitha's is evil. I can see Wes doing it as he wants to get revenge of Tabitha and Imogen to avenge Chip's death and his name due to the SA.
It’s definitely not dr. Sullivan! She was not evil in pretty little liars, she literally is there to help the girls cope! It’s either Wes, or it’s literally someone from Archie life