What if Lancelot is actually on Arthur’s side and they manipulate Snow and charming together to get them separated and to get the dagger. Isn’t it a bit weird how Lancelot shows up and Snow immediately confesses Emma is the dark one? And this is right after David admits that he and Snow met Lancelot once? Might be a crazy theory, but I wouldn’t be surprised if that happens.
I can’t see this happening, when Lancelot genuinely helped out Snow and Charming, and became good friends years ago. Yes he initially was a sword for hire who captured Snow for King George, but he didn’t know that George was going to poison Snow’s fertility. He regretted it, and did all that he could to make up for his mistake.