Can my marriage survive an affair?

I am 43 and have been married for 15 years.  We have three children together and are a happy couple.  We have a great life together and I have never contemplated stepping outside my marriage.

However I have met someone through work whom I am wildly attracted to.  It was all so innocent in the beginning. He is a client that I didn't see often and had a business relationship with.  Recently we have had some issues with his account and we have been spending a lot of time together.  Nothing has happened and we have both kept it professional although I would be lying if I didn't say I get excited to see an email or text from him flash across my phone.  It seems like there is always something to talk about work wise and when there isn't we both make things up.

Recently we have started having lunch so we can discuss strategy.  We both know its a cover for wanting to see each other and we both know its wrong yet we can't seem to stop.  Sometimes our hands touch by mistake and we are both unable to speak.  The sexual tension is so great that all we can do is stare at each other.  We try and talk about it but we can't.  We both know that we are heading in a dangerous direction and we both know we should stop before something actually happens - but we can't or we don't or we won't.

Obviously this has weighed heavily on my mind.  Do I not love my husband? Am I not "In Love" with my husband? Is this normal in a marriage? I go over and over it.  I do love my husband and I don't want a divorce. In fact I love our life together and I love him.  But I do want to have sex with someone else.  I want it so badly that I cannot think about anything else.  I fantasize about being with him all the time and feel if we do it  "just once" it will be out of my system.

I sit up at night wondering: Can my marriage survive? Does he ever have to know? Is it really such a big deal? I know its wrong - and I know I would be devastated if the tables were turned but I can't help myself.  I believe that so many couples have had "just sex" with people other than their spouses and carry on with their marriages.  I am just trying to figure out if I am one of them!

L.W.