It is more than possible... they are ton of unhappily married people everywhere. I have a theory people can change after ten years or so, and that can change a relationship. The person you married can be a different person in ten years.
From my experience (it is my own so there may be a lot better advice out there), a lot of married women feel neglected and they want some attention badly. Some of them just want someone to talk to.. all that stuff.
On the other hand when women get into their 40 s and 50s they get really horny.... and there are a lot of available unmarried women in this category. From my own experience again, with some of them it is hard to go slow, SOME tend to latch on.
From my own experience, dating sites like POF are not good..... you waste so much time and you have no idea of chemistry, etc. Much better to go to social stuff. Funny thing, once word gets out among women, I always found many others. It was like they told their friends you are available. I know many of you hate anything to do with work situations , but you do get to know what people are like at work. I dated women at work... everyone knew my home situation at work. Met through friends and that sort of stuff too.
Now down side.... everything may be secretative. That may be exciting at first, but personal taste dictates for later. Personally, when I had a long affair, the woman I was with snuck out, but she didn't really give a fuck about hubby finding out, and just didin't bother hiding stuff. I was in a severely estranged, so I never really had to worry about hiding anything. I could come home 4 am or whatever.
Anyway, one day her hubby did find a bunch of stuff, and even though I knew their relationship was bad (they did eventually break up), I didn't feel too good about myself the day he found out. Strangely enough, it didn't phase my girl-friend a bit.
Advice from me - I was with a truly awesome woman when I settled on one person and it was a part of my life I feel really good about, and the experience was great for me.
However, I really mean this... look at your marriage. Is it worth it? If it is, really think twice about doing this sort of thing. I do know if I was married to someone I really cared about I wouldn't be screwing around. That is just me, and I don't judge others. On the other hand, if it no loss for you to risk your marriage, that is a totally different story.
That is just some word from the trenches. One other piece of advice - find a really good SP.