You'll never know anyone's marriage but your own. And even then, you'll only know half of it.
This observation is not only very accurate and astute but it also shows that even in a great marriage, you only really have your own perspective on it. Marriage, and relationships, are entirely subjective, in that we can only judge how we feel. We can interpret the way in which our significant other acts and try to translate this behavior into feelings, but ultimately, we only know our own heart. We are only guessing at what is truly in someone else's. This is why it is very hard for a person to say that another couple have a good, or a bad, marriage; even a marriage that looks bad, or unusual, to the outsider, might make both parties in it extremely happy.
The quote also emphasizes the loneliness of each of the characters in the novel; even those who are married are in some senses alone, because only they know their own feelings, and can not judge even the closest of spouse's feelings one hundred per cent.
How could she explain that this city was a graveyard? That they were walking every day through streets where there had been a holocaust, a mass murder of neglect and antipathy?
Fiona is frustrated that the AIDS crisis in Chicago is largely being ignored, because people believed that there was no crisis in the Windy City. The AIDS crisis, to the observer, was something occurring in Los Angeles, San Francisco and New York, because that was what the media portrayed. In Chicago, the gay community was being decimated but people were not understanding that. Fiona is frustrated and angry because she feels that if the deaths were occurring because of a deliberate intention - a mass shooting for example, or ethnic cleansing such as we see in a war zone - people would be aware, and taking notice, and actually make the effort to get involved, but she feels that the epidemic is getting worse because of ignorance, and of a neglect of a community that needed help.
"The thing is," Teddy said, "the disease itself feels like a judgement. We've all got a little Jesse Helms on our shoulder, right? If you got it from sleeping with a thousand guys, then it's a judgement on your promiscuity. If you got it from sleeping with one guy, that's almost worse, it's like a judgement on all of us, like the act itself is the problem and not the number of times that you did it."
Teddy realizes that AIDS is seen less as a disease that needs to be treated and more of a punishment for being a gay man, whether a promiscuous one or not. If you are promiscuous and you contract the AIDS virus then the disease is seen as something you have brought on yourself by sleeping around. This is more of a judgement on the person, rather than the community as a whole.
However, he also observes that it is far worse in a way if a person becomes HIV positive after sleeping with only one person; admittedly it does not cast so much of a shadow on their own sexual habits or morality, but it is actually worse for the community as a whole, because it gives the impression that sleeping with another man is a game of Russian roulette that one is almost certain to lose because just one encounter is a death sentence; this implies that all gay men have the virus. Teddy feels that the reason the epidemic is being seen only as a "gay problem" is that it enables people to pass judgement on the person who is sick, rather than addressing the disease as a medical issue.
