Dante's plan

In the sneak peek on Talking Dead it showed Rosita coming to Saddiq's room right after Dante killed him and Dante nervously answers the door and is trying to keep her from seeing Siddiq's body, then you see Siddiq open his eyes and become a walker.

Plus in the preview you see Dante being put inside the cell, so i don't think he is able to make it look like a suicide.

I think Dante may have been thinking about coming over to the Alexandria side. He seemed to be genuine about being a friend to Siddiq. The stuff he did in the last episode was all about covering his own tracks. He didn't want to kill Siddiq, but he also knew Siddiq had figured him out and would tell everyone else.

One could suppose that Lydia never knew his face in the first place because of the masks. As for he not noticing Lydia...? Not sure. Maybe they just never crossed paths. She wanted to be in the cell, and then she bailed. Also, she was never sick, and, IIRC, Dante wasn't among those to tend to her after she was jumped.

Is he, indeed, a plant by Alpha? Is he Alpha's true "#2" and actually knows the truth about Lydia? Nah, doubtful. Did he say "fuck this" to the whisperers lifestyle and legitimately want to change and become part of a community, but, as winslow said, because of his mouth tic, had his true identity discovered by Siddiq and was left with no choice? Possible. He did seem genuine about regretting having to kill him.

I quite enjoyed this twist/episode. I know a lot of people didn't, but it's undeniable that TWD has long been in the "trendy to hate" category. I've been right there with people when the show does really, really dumb stuff, but I thought this was decent. Something worth talking and speculating about, at least.

He learnt medical from Saddiq it seems, anyway next episode will reveal how he infiltrate them judjging from the trailer

I am curious what sort of uprising there could be with the Whisperers when Lydia shows up after Alpha told everyone she killed her.