Why is this a "dark" moment? I think it's illustrative to see how this is set up.
Gemma is TOUGH. And she loves her men, and above all doesn't want to cause them harm. (And she knows they're dangerous when they're riled. :)
She doesn't "whine". She doesn't seek support. She doesn't ask for help. She is always in charge. That's her value system. Telling about this is against her own personal code. It's weak.
That's set up ahead of time. So when she is moved to tell this secret, to reveal her vulnerability and what she thinks of as her shame (she knows it's not her fault, but she thinks she was stupid and weak to let it happen), it's a very difficult choice because it goes against what she believes she "ought" to do. She ought to be able to handle this. And she sort of can (her sexuality is profoundly affected by the secrecy, and her relationship with Clay, so it's not unmixed-- and shouldn't be). Her decision to tell is made from love -- trying to reconcile Clay and Jax.
Clay, btw, has a similar journey. We of course think the husband of a rape survivor should act with love and compassion and never scorn her (and we're right). But by his code, or the club's code, which Gemma knows and actually supports, he should reject her now. That is, it's HIS value system, not ours, that makes this "dark", makes this a difficult choice for him. (He too acts with love, fortunately, but the writers quite rightly make this take a bit of time.)
But it's OUR value system (he should act with love) that determines, I think, that this is the right decision, even if it's the 'wrong' one by his own pre-existing value system.
Brilliantly done. But this is important-- we have to set this up. The action has to be painful, difficult, "dark" for this to be a dark moment. What in the run-up, in the whole story and character development BEFORE the dark moment makes this dark for your character?
BTW, there's a very nice setup moment for Jax in this episode. His friend, speaking of Clay, says, "He's your father." (Clay has, apparently, been his stepfather for 20 years, and they do love each other.) Jax says coldly, "My father died on Hwy 580." (His real father.) That is, Jax disavows this relationship (he has good reason, also set up). And so his action in the end of the episode, where he puts his hand on Clay's shoulder, and stays there as Clay covers his hand and holds it, is that much more intense, as it's re-establishing his filial bond.