After Eretria spends her portion of the episode realizing what a great place Utopia could be and being genuinely happy there (probably the first time she has been in her life), it turns out that she was only brought there to be a Human Sacrifice so that the humans and the neighboring trolls could maintain their truce. A true Yank the Dog's Chain moment if there ever was one.
Episode 10 - "Ellcrys"
Wil and Amberle saying their final farewells, even more so because they get interrupted by the Dagda Mor and she has to leave before they can even finish talking.
Later on, Wil pressing himself against the side of the Ellcrys, begging Amberle to speak to him, and getting no reply.
Episode 2 - "Wraith"
Eretria's bitterness at Lyria for lying to her. While Lyria insists that what they had was more real for her than the life she ran away from, Eretria is too hurt to believe her and they part in mutual heartbreak. Especially harsh given that this is the second episode in a row that Eretria has found out that someone she loved has been keeping her in the dark, and that last season established her as having trust and abandonment issues in the first place.
Episode 3 - "Graymark"
When Riga is trying to get Allanon to tell him where the Codex is by slowly draining Wil of blood before his eyes, Wil bitterly tells him it's useless - Allanon doesn't care about him and so will never crack. Judging from Allanon's heartsick expression, he's wrong about the first part, but he still turns out to be right about the second - Allanon really would have watched Wil being slowly killed rather than betray his duty. It's hard to say which one of them to feel more sorry for, Wil for being failed by yet another father figure or Allanon for being hated by someone he cares about for doing what he regards as the right thing.
Episode 4 - "Dweller"
Will finding out what his father was like, a much better man than he thought.
Episode 5 - "Paranor"
Jax unwittingly leading the Crimson to Sheema and Desmin, leading to Desmin's death and a grief-stricken Sheema telling Jax that she never wants to see him again.
Episode 6 - "Crimson"
Wil's Blatant Lies to Shea about how he will become a great father, all while knowing that for all Shea's sweet-naturedness and good intentions, he's going to end up a drunken, half-mad wreck who will ultimately abandon his family for their own good.
Ander's death, especially the fact that Riga managed to get the upper hand by playing on his insecurities. Even after everything he'd done and accomplished and sacrificed, he died still believing that he was unworthy of bearing the crown and probably spent his last moments alive feeling that he'd failed just like he knew he would.
Episode 7 - "Warlock"
Tamlin's and Jax's conversation as they are waiting for her to be brought to her execution.