This wasn't too dark but I remember watching this episode of The Flinstones when Barney and Betty adopted Bam Bam. Barney had spent a lot of time with Bam Bam and grew to love him dearly

But eventually, (I don't remember the context for this) Barney had to give him back, and he said this tearful goodbye to him. I remember suddenly crying when I saw that as a kid, and I didn't realize why until I was older

The end had Barney tying himself to a rock and was ready to throw it down a bridge, when Fred comes in and tells Barney the good news that they can go through with adopting Bam Bam. So at least it ended on a positive note, but that was still pretty dark lol