I too feel frustration at times. I've been married for 15 yrs and have two great kids. My wife and I are close but the sex is nowhere near often enough for me. Her sex drive is just way lower than mine, used to be only a little lower but having kids changed things, including her body.
Now for the past year or two my wife has been on prozac and is much happier and more relaxed -- but also gets tired earlier and so we have even less sex as I am more of a late-nighter. So we have our issues. I've discussed it with her and she's not willing to drop the drug yet.
So I get off more on my own by coming here and chatting with women on yahoo and sometimes guys too, just for company. I love showing off. Sometimes I cum harder than with my wife. I think a lot about getting some on the side but always feel in the end it would be rather empty and not worth the bother or the risk. I could be wrong.
Anyway, just another example and I'm sure I have lots of company in this regard.