It gets worse if you put it in perspective. Gil spent most of his life hoping for a girl who could understand his crazy Sparky ideas. He gets his wish in form of Agatha, spends only a couple of days bonding and falling in love with her and then all of this is ripped from him when she “dies”. They weren’t even so close, like Gil himself admits a few times, but the possibility of what they could have been is enough to send him down the spiral of depression for next two months.
A subtle one for me, but when Agatha stumbled onto Dr. Dimitri's teddy bear stash, and he's begging her not to tell... "He doesn't know! It's my last secret! He's taken all the others, but not them! I've kept them safe!" Seeing the scars on his head, and then finding out that Baron Wulfenbach has been lobotomizing Sparks to see how to deactivate them makes it particularly sad to this troper...
What makes it even worse is imagining what would happen if Wulfenbach found out about the stuffed bears. No matter what Klaus' reaction would be (either to let him keep them or take them away) it would be heartrending.
Gets worse in the novelization - when they're escaping Castle Wulfenbach, Krosp drags Agatha and Theo off to find him. When they do, Vapnoople reveals that the bears are supposed to be his new army, but though he still acts like a Spark, he isn't one anymore, and they're forced to leave without him.
Krosp calls Vapnoople Papa. And is clearly upset when he has to leave without him after promising to take him somewhere safe and says he'll return.
And it's been confirmed, that Vapnoople wasn't just talking about the STUFFED bears. Everything the man went through, and he managed to keep a truly enormous secret...and they're made to obey Krosp, confirming the man saw the cat as a great enough creation for that responsibility, too.
How about in "Agatha vs the Jägers"? Seeing a superhuman immortal hunter monster collapse into tears because he found the last scion of the family he loves and swore to obey, plus gets to go home? Their cause was literally hopeless...
Ognian: Ve haff missed you! Please, please be real! Agatha: Shh. I... I am.
Othar's Twitter, of all places, has one of the sweetest and saddest relationships ever.
Thesetwo pages, as Barry gives Agatha her locket. Made even worse by the fact that Barry Heterodyne, who freaks out even Lucrezia Mongfish, the OTHER, is crying. And that young Agatha seems to be just as intelligent as she should be, rationalizing Barry's statement of "it's science" to "Ah. You mean you'll explain when I have a sufficiently advanced background education." Necessary or not, what Barry did to Agatha was horrible.
The little waspeater babies lost their mommy.
Looking at Ruxala, the wasp eater wrangler on the crashed Vespiary Squad ship that Tarvek boards, bawling while clutching two dead wasp eaters and surrounded by several others.
The look on Klaus's face here. He hates what he's doing to Gil, but there's no choice...
Its brief, but Prende looks absolutely devastated when it looks like Andronicus is going to abandon her in favor of his Roaring Rampage of Revenge. Thankfully, Agatha manages to convince him to take her with him.
Dimo revealing that the Jägers used to discretly follow around the Heterodyne boys on their adventures. Barry eventually noticed and Bill ordered them to not follow them on their next adventure, basically because it's hard to make it as a hero when you're being protected by the minions of your notoriously evil ancestors. That adventure is the one during which they vanished.
Dimo: Ve should have been dere. Ve should haff gone vit dem.
The next page dicusses the reason they were ordered to not follow, and has Dimo outright suggest Agatha she may want to let go of the Jägers at some point if she wants to be accepted as a heroic Heterodyne. Agatha's reply to this belongs both here and in Heartwarming Moments.