Sam's tearful goodbye with his imaginary son in "Go Make". The son says "see you in a few years," but as of Sam's guest appearance on Frasier he still hadn't found someone to settle down with.
In "Pitch It Again, Sam," Sam gets a chance to pitch in an exhibition game. At the stadium, Sam comments that the only thing missing from this great opportunity is Coach. Carla tries to do an impression of Coach to motivate him, but she winds up crying - twice.
Carla: I just miss him so much.
Diane's recounting of her relationship with her beloved cat Elizabeth, whom she's found out has just died, in "Let Me Count the Ways." It gets progressively harder and harder to listen to what she tells Sam without breaking out in tears of our own:
Diane:(Sigh) Well, she was the only one in my life who was always there.... When everybody else was mad at me, she always liked me...when I'd—hide when my parents argued, she'd come with me, and...whenever I was sick, she never left the bed until I was well again....
(Tearful Smile; Sam smiles encouragingly; Diane walks to the desk)
Diane: And then, um...when I was...twelve years old, my parents separated. (Swallows) It was—maybe the worst night of my life.... Believe it or not, I actually thought about throwing myself in the lake. But—then I...looked down at this cat in my lap, and thought, "Well...who would take care of Elizabeth?" (Tears finally escape)She saved my life that night! And I know it's—crazy, and it's irrational, but...oh, Sam, I can't help thinking that last night, when her time came, she must have wondered where I was....
It's more than even Sam can bear, as he starts shedding some Manly Tears at this.
"Sorry, we're closed." (*adjusts Geronimo picture, walks to the back room*)
In "Coach Buries A Grudge," Coach prepares to host a memorial service for his recently-deceased best friend, only to find out moments before that he attempted to cheat on his wife. Horrified and disgusted, he tears up the speech Diane helped help write, deciding it'd be more fitting to rip into him in front of the assembled guests and tell them all just what a terrible person he really was. Against Diane and Sam's urgings, he takes the podium...
Coach: I had a beautiful speech written for me here but uh.... I'd rather say a few things from my own heart about T-Bone Scarpiggione. T-Bone Scarpiggione was a son of.... (Trails off, looking at T-Bone's picture) That man was a son of a.... T-Bone Scarpiggione was a son of an immigrant. And like most immigrants, he was a human being. Human beings make mistakes. We're just not perfect. But I'll tell ya what isn't a mistake; (Choking up) To love someone and forgive him.... No matter what his shortcomings. That's not a mistake. I loved that man... And I forgive him. And I know that for the rest of my life... Every day there's gonna be a moment where I'm gonna miss him. That's all I got to say.
At that point, all of the guests at the wake declare how T-Bone hit on (and actually slept with) their wives too. They all go to lynch his cardboard picture, before Diane starts singing "Amazing Grace" - causing the others to stop and join her, finally forgiving T-Bone.
Diane's request for Coach to "watch over Sam" in "Cheerio Cheers" is doubly this when you realize that not only would Diane not see Coach again prior to his death in-universe, Coach's actor Nicholas Colasanto died only a few days after the episode was filmed.