It's only cheating if you're breaking a rule to not sleep with other people. Swingers aren't cheating (assuming they're respecting any agreed upon boundary) when they're having an orgy for example.
A bi man with a wife and a family could very well be having sexual encounters with men once in a while with the agreement of his wife (who could well have her own stuff going on too) and it could be a very healthy thing in what is a fulfilling relationship for both parties.
You might be right morally, but in a lot of countries it is still the case that 'not having sex with other people' is a compulsory clause of the marriage contract. So legally it's a little bit murkier.
People have been advocating for marriage contracts that are a bit like the CC license, where you can pick the parts that you agree on.
Marriage is on its way out in many places. In my region of Canada (Quebec), less than 50% of couples with kids are married. That number keeps going down every year.
(There are some automatic protections in the event of a separation.)
Factually speaking yes but practically speaking gay/straight people tend to be doubly touchy about their partner "playing for the other team" so to speak. Which... I mean, cheating is cheating is cheating lol
A wife might be accepting of a husbands bisexual adventures and not consider it cheating. What about her parents, his parents, children, family, coworkers, congregation, community, etc.
I wasn't speaking directly to that, moreso that secrets have value. Some people would reveal their secrets rather than be controlled with them, others will define the value of their secrets by what they're willing to do maintain them.
It's easier for a straight person to pass off a straight dating/hookup site vs. a "straight" married person on a gay/bi site. The straight person can just say they used the site before they were married, etc. whereas there's no such excuse for the gay site.