The movie is totally is about being uncomfortable with being gay and trying to accept yourself. Take the narrator, he’s obsessed with decorating and fashion and he straight up tells you the only place he feels safe and secure is around a bunch of men without testicles, men who can't penetrate him, but one's he's free to hug and have close contact with. His favorite guy at these meetings is a man with breast. I don't know if you're familiar with how people uncomfortable with their gayness rent porn, but it usually goes from straight to transsexual to gay. So he’s found this world where he can get the male affection he craves without having to admit there is a sexual component to what he’s doing. He also goes to meetings with women who want to have sex with him, but he finds them disgusting. Now the narrator says they're gross because they're dying, but we also know he's an unreliable narrator. He then meets Marala. She is a flat chested manish looking woman who he has a great rapport with and who is sexually interested in him. He’s lost his excuse for not dating women, so he starts fantasying about his gay ideal.
Tyler is gay ideal, an extremely fit looking man with a Laissez-faire attitude towards moral taboos that dresses head to toe in couture Versace. He uses this personality to attract other men into a fraternal organization based around secrets and touching each other. Yes, he eventually has sex with Marla but its unconventional sex (anal and fisting). She say’s I haven’t been fucked like that since grade school implying he’s clumsy like a child or a child molester (he hasn’t ever had straight sex). The narrator actually goes so far as to mentally deny that he’s the one having sex with her and is disgusted when he finds out, proving to himself that he’s gay. At this point the movie turns he tries to get rid of Marla by sending her away, he’s fearful if other men find out his secret they’ll castrate him, taking away his ability to have gay sex. He confronts his gay idea realizing that he doesn’t need an ideal just a man. The end of the movie has him destroying credit card debt and taking Marla’s hand, he’s forgiving his past, accepted his homosexuality and forging a platonic relationship with Marla.