many characters in It's A Sin.
At the beginning of the episode, Colin is stunned to find out that the tailor at which he works is sending him along with his boss, Mr. Hart, on a work trip to New York City. Viewers instantly suspect an ulterior motive, given Hart's lascivious treatment of Colin in episode 1. And with no Henry there to look out for him, Colin is likely in for a rough trip. Colin's friend Jill requests a favor: find some literature on the AIDS virus in the United States and bring it back to London. One night of the trip, as he's again harassing Colin, Hart spots the AIDS-related newspapers and magazines and abruptly leaves the room. On their return to London, despite being told the trip went well, Colin is opaquely told he's "no longer employed," as of that moment, without reason. As Colin leaves, he tries to catch Hart's eye to beg to stay – despite Hart's lecherous treatment of him – but his boss entirely ignores him.
It's yet another subplot in the series that demonstrates the prejudicial treatment of gay men by society in the 1980s and the stigma surrounding the AIDS virus at the time. When Colin is let go from his job, it lays bare his employer's terrible motives for keeping him as an employee – Mr. Hart wants to continue to set up situations where he may harass Colin – and also the fear and misunderstanding people felt at being around someone who might have contracted the virus. This misunderstanding is shown through other characters' behavior, too, including when Jill washes, then destroys, Ritchie's mug after Gregory uses it when he visits the Pink Palace. It's the same fear and misunderstanding that will lead to Colin being locked into a hospital ward by himself in It's A Sin episode 3.
Though It's A Sin is set in the 1980s and '90s, AIDS stigma and discrimination are still very much alive in places around the world today. LGBTQIA+ people of all genders experience ongoing discrimination in the workplace and other areas of society, including in their own families – like the treatment Ritchie and Roscoe receive in the series. There are now options for effective treatment of HIV/AIDS to address their effects and to reduce transmissibility, and those who test positive for the virus can lead mostly normal lives, but a solution to a problem doesn't mean stigma and prejudice disappear.
It's A Sin depicts many hard truths faced by the LGBTQIA+ community, both related to the AIDS epidemic and separate to it, and Colin's experience in his workplace is just one example of how the people around gay men can take advantage of or discriminate against them for no reason other than prejudice. While this has improved in many places, it's an ongoing issue about which It's A Sin has helped raise awareness.