I am a 52 year old married man that has fallen in love with a 40 year old female co-worker who is single and a mother of two teenagers.
I do not know how or exact when I started to feel this way ( like a 17 year boy ), but it has been more than six months. We have a great relationship at work, but I do not know how she feels about me.
Some days I think she really has feelings for me and other days nothing? This is driving me crazy. My question to you is Should I tell her how I feel or say nothing and hope this feeling dies in me?

No, you are married and if you really feel something for her there's nothing you can offer her right now (like a true relationship) and she deserves more than a "behind closed doors" relationship.

That's tricky. If you tell her how you feel and she doesn't return the feelings, your relationship could become awkward. But on the other hand, she might be waiting for you to make the first move. Could you invite her out as a friend and see how it goes?

You're married.

End of story.

Why don't you ask your wife what you should do, Steve ?

I'm sure that she would more than happy to help you with the right answer.

Wow. Somehow I totally missed the part of you being married. I take back my previous advice. If you're married, you have no business even considering making a move on someone else

You are married. That means that you are NOT available.

Leave her alone and let her find someone who's single... I'm sure she doesn't want to be a homewrecker.