For me it was just about everything with Kasumi in Far Harbor. When I both heard and felt the grief in this family after their daughter left home because of an identity crisis (and because of those filthy droids taking advantage of her insecurity), I wept. When I found out that she's run away to my childhood home (both IRL and my character's), it made things somewhat more personal, and a very somber piano tune began playing in my heart. And when they reunited, that was just a very touching moment that made me misty-eyed and gave me the sniffles. I turned down the reward because in my heart I felt I'd done the right thing; plus getting to eradicate clankers and those damn dirty cultists (both of whom were threatening the descendants of my people) was a reward in its own right.

I actually teared up quite a bit when I was forced to confront Shaun on his death-bed after setting the Institute to self-destruct. Just knowing that someone, your own son put their entire life's work in your hands... And you scorned it in the name of your own ideals.
I don't know... I kind of felt like I was betraying the unspoken rule that a Father has to provide for his children, that as a parent it's your duty to make sure your children are happy / fulfilled... But then having Shaun lay there trying to understand your decision as his life crumbled around him... That really got to me. He really did want to do the right thing.

Imagine helping create something as amazing as the Institute with the intention of saving the world... And then your only legacy is a giant crater in the middle of Boston and an ever-lasting reputation as a menace.

That scene is probably one of the darkest, saddest, and well-done scenes in a Fallout game. Honestly, if the leader of the Institute wasn't your son, the death of the Institute wouldn't be such a hard decision. A father that has even the smallest amount of love for their son would probably develop PTSD if they were put in that situation. Seeing your son on his deathbed,
telling you that you're the reason for destroying his dreams and dying knowing that his dreams will never be accomplished because of his father and that he will be seen as probably the next Master.
I don't know if I can live with myself if I was put in that situation.

I think Nuclear Family is the sadder ending, being the dialogue is better written and Father doesn't call you a hypocrite in every dialogue option.

My reasoning is that in Nuclear Family you work so hard to save your son, then you betray your own morality to work with your son, form a bond with him and take on the world, as Father and Son. Unfortunately, even then you lose the very son you sought to protect. It nullifies everything you did before and leaves the SS with everybody in the Commonwealth hating and fearing him. Even Piper and Nick start to perceive him more as an evil menace than the hero he was previously.

Then, if Nuka World is canon, the SS becomes a power-hungry maniac and raids the Commonwealth, betrays the Minutemen he fought with and becomes a tyrant.

While I did not straight up cried, I was sadden and shock to learn that Shawn was part of the Institute.

The first time the last minute man informed me of a settlement that needed my help...and the fine gent took the liberty to mark it on my map. I believed I was going to make a difference in the commonwealth

Installing the mod that allowed Preston mufukin Garvey to be shot in the FACE before he ever got the chance to send me on a wild goose chase through the wasteland.

The decision surrounding Dima...I mean since my character is a gen 4 synth...Dima was like great grandpa...It's the only time where I "cheated" and made a choice...and then seeing it through reloaded my save and chose the otherway...

@dantaefetticus Man, both you and @IIHawkerII totally nailed it. That part of the game is always a major turning point for my character, in which he becomes cold and bitter just like Kellog. It makes the narrative in my head easier for why he ends up turning into a raider later and betraying the Minutemen and enslaving the Commonwealth. He just has no fucks to give at that point.

My second character Hannah's husband was executed, her son Shaun was stolen from her, and she later "had" to kill Shaun (I shot him in the face after finding out what he was responsible for), so her family was destroyed and she truly was the Sole Survivor. So that obviously sort of broke her will; that, combined with the violence in the Commonwealth, kind of molds her into a cold-blooded predator...

...But there's still good inside her. Helping put a lost and broken family back together again was perhaps a reminder that there is still love and kindness in the post-apocalypse, and as I'm currently working on "Nuka-World", which focuses on being an evil Raider dickhead in charge of three clans of psychopaths (one takes almost sexual pleasure in killing people, and another enslaves people and animals and keeps both in cages with shock collars around their necks), my endgame is ultimately to get the meat and potatoes out of the way (the quest "The Grand Tour" pretty much is the Nuka-World expansion) and then put a few (hundred) rounds into all of the Raiders in the park.

So Hannah; a mentally-fragmented woman who was sucker-punched by time and lost everything she had, but gained an unquenchable bloodlust that helped patch up her heart with each life she took, but on the strict condition that said lives were of people and creatures who threatened the innocent.

tore every circuit and cable out of DiMA with my bare hands