When Bruce futilely tries to save a man's life, while the man's wife and child are watching over, begging for him to be saved. It's one of the few good things Bruce tries to do in the entire story with no pretense of manipulation or self gain and it just doesn't work.
There is also the fact that Bruce's inner dialogue refers to the dying man as "the boy", despite the man being in his forties. Bruce was having a full-on flashback to the tragic death of his brother and only friend as the whole thing happened.
The disastrous results of Bruce and Blade's trip to Hamburg that send Bruce past the point of no return. Bruce slips ecstasy into Blades' drink, and everything goes fine for a while; Blades begins dancing around and seems to be enjoying himself. Then Blades does what anyone with little to no experience with street drugs being heavily spiked would do: he starts freaking the fuck out. Bruce tries in vain to get Blades to calm down but when it doesn't work, he gives up and Bruce is left hiding in another room, desperately trying to drown out Blades' screams. After an unsettling moment of Bruce hallucinating his reflection being a demented pig-man, he stumbles through the streets in a haze, bumping into people, at some point attempting to start a fight, before he eventually falls to the ground, whereupon he looks up and mistakes a woman for his estranged wife. Bruce desperately grabs the stranger and pleads for her to tell him where their daughter is, begs for a second chance, and then the woman slaps him away from her, seemingly breaking him from his trance. The scene ends with Bruce meekly walking away, looking like a miserable, lost puppy.
Bruce tearfully watching a home video of Carol and Stacy in the film.
The scene at the supermarket where Bruce found Carole and Stacey with another man (implied to be Carole's new husband). Bruce tries to call Stacey only for Carole and her new husband bring her away from Bruce. At this point Bruce realises his life already pointless.
Bruce's breakdown during his argument with DS Drummond after he realizes he's hurting her, where he laments about how he used to be a good person and tearfully admits that he knows he's going insane and that his wife left him for reasons he can't even remember. Unfortunately, his demons grab hold of him again as he hallucinates Drummond as a witch and screams at her to go suck someone off and to "stop playing the amateur fucking psychologist" and storms out of the station, continuing his downward spiral.
The ending, Bruce loses any hope for redeeming himself and commits suicide with the scarf his wife made for him in a vain attempt to get revenge on her after leaving a tape apologizing to Blades, capped off with Clint Mansell's cover of "Creep" by Radiohead playing in the background. You would never expect to shed any tears over a misanthropic, racist, sexist, homophobic, corrupt sergeant detective but lo and behold.
Bruce's story in general is a heartbreaking tale. He was a Child by Rape and as such was ostracized from his home village, raised by an abusive father, spent his life as The Unfavorite to his younger brother, has to live with the guilt of accidentally(?) getting said brother killed, as well as accidentally killing his first love, then he loses his wife and daughter, which seemed to be the turning point towards his final downward spiral and anytime he tries to be good or nice to anybody it only backfires, leading to him continuing his unhealthy coping mechanisms of drugs, alcohol and sex. The story is a beautifully, realistically bleak portrayal of an intense, untreated mental illness and it showcases all of the issues that come with it. Bruce really had no chance from the start.
