Morality
One of the key tenants of the Conservative party in the U.K. is compassion and giving people the opportunity to succeed. Nevertheless, because of Nick's sexuality (which he can't change), he isn't afforded the same opportunities as everyone else, going against the Conservative's push for compassion.
Toby Fedden
Nick Guest ironically has a crush on Toby Fedden, despite Toby being decidedly straight and Toby not particularly liking gay people. Usually, people are not romantically attracted to those that threaten their very existence.
HIV/AIDS
Despite knowing the risk of having unprotected sex with men (and HIV/AIDS), Nick continues to have sex with men, putting him at profound risk. Generally, when people are able to avoid risk, they do just that; Nick doesn't and ultimately gets HIV/AIDS.
Nick's relationship with Leo
Despite the relationship of the time, Nick has a relationship with a young black man named Leo Charles. During the 1980s, many people were scorned for being in interracial relationships. Surprisingly, Nick didn't care and continued his relationship with Leo.