Where did the good go?

Things have shifted. No longer are people asking me if I'm engaged or married. No, and, compared to what I'm getting now, I wish they were. Now things have changed and my friends and colleagues have begun trying to convince me to get a lover on the side. I am completely appalled. Honestly, what the hell? I don't condone cheating, and I value monogamy, not to mention trust! When I tell these people that I can't do that, they ask why and I tell them that Brad trusts me and would leave me if I were sleeping with someone else. They seem to think that either 1. he doesn't need to know, or 2. I would be justified in seeking sexual gratification elsewhere because "a girl's got needs".
I honestly don't even know what to do with these statements.
First of all, saying "he doesn't need to know" is possibly the stupidest thing I've ever heard. Of course he has to know. I trust him and he trusts me and if I were to go sleeping around on him I would feel awful. I mean, really truly awful inside, because I would know I had betrayed his trust and furthermore that our relationship would be a lie. If a person withholds information from their partner that they know would make their partner leave them, then the relationship is a fraud.
Second, saying "he doesn't need to know" is not actually the stupidest thing I've ever heard because the "a girl has needs" takes that prize. If we have regressed as a species to the point where hedenistic behaviour constantly wins out over monogamy and morals, then...well...I don't know what to say. I'm ashamed to call myself a human being.
So....the irony of the situation is the only way to get people off my back and get them to stop telling me to cheat (which besides, in NONE of their business), is to lie and tell them we're close to becoming engaged and I don't want to risk the bling. Apparently the prospect of a diamond is the only thing that people consider as a reason to refrain from indulging in extrenuous sexual acts.
What have we come to?