So at the beginning, Merlin was facing off with the current Dark One of the time.  He says, âYou destroyed her, the only woman I ever loved.â And he looked sufficiently heartbroken about it as expected.
But wait.  He gets determined, saying, âI will destroy youâ and raises the dagger to kill the Dark One.  He looks angry almost, maybe even disgusted with what the Dark One has taken from him.
THEN ALL OF A SUDDEN HE FREEZES AND MAKES THIS FACE.
It is a complete shift from his determination. Â Itâs almost like realization. Â
And the only thing happening is the Dark One staring back silently at him, and we donât see the Dark Oneâs face at this moment of whatever he is realizing.
So immediately after making this face and pausing in his quest to destroy the Dark One right in front of him, Merlin says something that Iâm fairly certain was âMy god!â or something along those lines that further shows he is realizing something like maybe he is realizing his actions arenât right.  Then he collapses and drops the dagger!
If he is holding the dagger, we know he has complete control, so the Dark One did nothing to make him drop it. Â However, when he does, the Dark One immediately grabs it and holds it up to his neck as though to kill him.
Merlinâs life is literally in TOTAL DANGER against the darkest magic ever.  He isnât fighting despite being an even more powerful sorcerer.  He doesnât even look scared.  He instead looks COMPLETELY AND TOTALLY DEVASTATED and says, âI miss her.â  He is in what could very well be his final moments and he is choosing to lament his lost love instead of trying to survive.
Then, of course, the Dark One uses that heartbreak to collect this tear.
Why does this matter, you ask? Â Because what if the original Dark One IS THE LOVE THAT MERLIN LOST? What if his love was taken by the darkness, and SHE BECAME THE FIRST DARK ONE? Â She became this darkness as a result of something he didâ maybe even her trying to save himâ and in that moment he realized that he had completely lost her to the darkness. Â He had his realization in that moment that he couldnât destroy her because he made her that way and still loves her, so he canât see her as this totally even entity, even though sheâs gone. Â He is crying a tear of his greatest heartbreak and giving up on fighting because he lost her to the darkness, he is telling her he misses her, and he knows thereâs nothing that will bring her back.
Now Emma is the Dark One (also turning people into trees, just saying). Â Now Emma needed a tear of heartbreak and her first thought was Regina. Â Regina, who she became the Dark One to save. Â Regina, who has powerful magic like Merlin, who was trusted with her dagger like Merlin, and who would probably end up on her dying breath still unable to destroy Emma because she still sees Emma and not just the darkness.Â
