In my travels through social media over the past several years, especially on Google+, I've come across a phenomenon that I've come to affectionately refer to as "MINO" - Marriage In Name Only.
For whatever reason, women whom I've met on social media have a tendency to be willing to confide in me - probably at least in part because I actually happen to be a trustworthy person, and never, ever disclose private information that I am entrusted with to third parties. And so I end up finding out about their relationships.
I wouldn't say there's a "typical" MINO; they're all a little different. One woman, a religious Baptist, confided that she hasn't been sexually attracted to her husband for over 20 years, even though she claimed that she "loves him". That's a MINO. Another woman who has a disabled child still lives with her husband but she really no longer loves him and the marriage is more or less "kaput". Another MINO. Another woman got married to her best friend from high school because all of her friends were getting married (peer pressure) but she discovered that she has never really loved him. That's a MINO! Another woman confides to me that she's married but there's just no intimacy or love any longer. Yep, a MINO!
Now you may notice that there is a common thread here: People are staying in marriages that aren't working; in some cases they are either unable or unwilling to work to "fix things", and yet they persist in staying in these essentially failed relationships. Now in some cases there may be a sound reason - usually it's children whom the parents feel need that "family unit" as they grow up. But in other cases, there is no good reason at all other than the fear of the unknown.
The net result of this is that there is a lot of "fooling around" going on, almost always surreptitiously.
Me, I was married to the same woman for 23 years, and only cheated on her once. It lasted about one day. But the ex wife turned out to have histrionic personality disorder, was making my life miserable, and so I got divorced.
The problem with all this "fooling around" is that there's no free lunch. It creates stress - stress on the people in the failed marriage, often stress on the recipient of the amorous advances by the man or woman in the failed marriage, and occasionally even stress on the recipient's spouse, if they are married - and believe me, yes - they sure do find out!
Being divorced and essentially free from this kind of guilt, at least for the time being, I can't really offer much advice other than this:
If your marriage isn't working, for whatever reason, try to fix it. Get counseling, whatever. If it can't be fixed, then if you can, accept that and get unmarried. Then you'll be free to fool around all you want -- without the stress and the guilt.