Hercules: All I know is you're the most amazing person with... weak ankles that I've ever met. Meg... when I'm with you, I don't feel so... alone.
Meg: Sometimes it's better to be alone.
Hercules: What do you mean?
Meg: Nobody can hurt you.
When Phil discovers that Meg is (reluctantly) working with Hades and attempts to warn Herc, Herc just goes into complete denial, leading him to accidentally hit Phil. The look of hurt on Phil's face right after this shows just how much this has affected him emotionally.
After Hercules loses his strength, Hades, Pain, and Panic humiliate him in front of Meg, causing her to cry.
Hercules loses his super strength after fully realizing his betrayal by Meg and his betrayal of Phil. Cyclops is yelling for him to come fight, and he goes.
Megara: What are you doing? Without your strength you'll be killed!
Hercules:*dully* There are worse things.
Hercules' Big "NO!" when he sees that Meg's been crushed after pushing him out of the way of a falling column. Sadly the mood does not improve as Herc gets his powers back and gets it off her.
Meg: Hades' deal is broken, he promised I wouldn't get hurt.
Meg's death. You get a lot of focus on her dying in pain with Phil beside her - and adults will realize she must be in agony. And then Herc's rushing back to try and see her before she dies (even though there's not a whole lot he could've done), while the Fates prepare to snip her thread. And she doesn't die in his arms. She dies and she doesn't even get to see him. And Herc arrives to see her lying there clearly dead, and pale, and limp. Herc holds her and starts sobbing manly tears, and she's just lying limp in his arms. You hardly ever see somebody actually dead on screen in anything below a PG-13. But here you're given a good thirty seconds to take in this heart-wrenching moment. You must cry. You must.
The end. When a constellation is created for Hercules, his trainer, Philoctetes is awed. Someone points out the constellation, saying, "That's Phil's boy!", and Phil sheds a tear of joy, having just realized his life's ambition.
Phil after it seems like Hercules dies along with the hydra.
Phil: There goes another one, just like Achilles...