Sexuality and sexual frustration are a common occurrence and theme in Silent Hill. The theme appears in nearly every game in some form or another, being more prominent in Silent Hill 2 and Silent Hill: Origins, with Silent Hill: Homecoming having the same theme as well. It is mostly absent from the first game and Silent Hill: Downpour.
Silent Hill 2
The theme of sexual frustration was first introduced in Silent Hill 2, in which James Sunderland's wife was hospitalized for three years due to a debilitating illness. During these years he watched his wife grow weak, bitter and, in her own words, ugly. This naturally had a profound impact on their sexual lives.
The frustration due to the lack of sexual activity between them manifested through the Bubble Head Nurses and almost all monsters in the game. The scene in which Pyramid Head appears to "rape" Mannequins, and later, a Lying Figure, allude to this.
The character Maria can also be seen as an extreme manifestation of sexual desires. Maria is healthy, beautiful, cheerful and vibrant. She is everything that Mary was not near the end of her life. Maria represents the type of woman James wishes Mary was and he ends up trying to replace Mary with her in the "Maria" ending.
The Flesh Lip is a possible representation of labia (vaginal lips)
The theme also appears in Fukuro.
Silent Hill 3
While Silent Hill 3 contains no sexual frustration as such, the theme is still present, though it manifests mostly in the form of the god forming within Heather Mason's uterus. Heather being pregnant against her will is symbolic of rape. Heather is a teenager and may be struggling with her own sexual feelings, while the part of her that is Alessa Gillespie knows the dangers of men.
The possible appearance of the Fukuro Lady and the Brookhaven Nurse can also be considered sexual, seeing both being abused at some points, the later being abused or caught and exploited by Valtiel on many occurrences.
The form of sexual frustration is mostly represented by Walter Sullivan's possible infatuation with Cynthia Velasquez, a woman that Henry Townshend meets in the Subway world. Sixteen years before the events of the game, Cynthia and Walter had a brief encounter on the subway. Walter approached her nervously and tried to talk to her, but she assumed he was a stalker and proceeded to humiliate him in front of her friends. The possibility of being infatuated with her is supported by how she is killed with the "Temptation" theme. Furthermore, Cynthia is shown as being promiscuous. Even at the age of thirteen, she was already going to night clubs. When she enters what she thinks is a dream, she promises Henry, the first man she meets, a "special favor" if he helps her, although what that favor might have been is unknown.
Silent Hill: Origins
The theme is much more prominent in Silent Hill: Origins than in past games, save for Silent Hill 2. Protagonist Travis Grady is a troubled trucker tormented by his past. When he was a child, his mother went insane and tried to murder him. As an adult, his problems with women becomes apparent. A fellow trucker tells him that he needs to find himself a nice girl, implying he doesn't have much contact with them. Monsters are noticeably affected by this, the Faceless Nurses being the most obvious, as well as the Two-Backs. Also, Lisa Garland plays a role in this, as she flirts playfully with Travis at times and it is implied that she and Michael Kaufmann have sex.
The Butcher also portrays his sexual frustration, as the creature can be seen slicing through the reproductive organs of his victims, specifically the sexualized monsters. It is unclear whether Travis once was a serial killer and committed these acts, or if the Butcher is merely a manifestation of his inner demons.
Silent Hill: Homecoming
During his time, he creates the delusion that he was a soldier, believing that he was in a hospital for wounded soldiers, rather than a mental hospital. He imagines that the nurses wear revealing clothing to comfort the soldiers. The Nurses in the game have noticeable cleavage and have a growing fetus in their womb, heavily symbolizing birth, which is a very powerful theme in the game.
Alex speaks fondly of the girls back in his hometown of Shepherd's Glen, as well as making reference to buxom females he sees during his tour of duty, suggesting that he is somewhat sexually frustrated.
Nora Holloway's monstrous form also bears many pairs of breasts. When Nora died, she was a teenager. The overwhelming amount of breasts as well as the vaginal area being covered may represent how she will never get to experience the pleasures and physical aspects of womanhood.
Unlike all other games in the series, there is a very real possibility for the protagonist to become a sleaze, which influences the ending. Harry Mason can look at pictures of half-naked women and act sleazy and promiscuous, and this will affect how the game progresses and the ending as a whole. Depending on his Psych Profile, characters can become sexualized such as Cybil Bennett.