A very important thing to remember first of all, is the marriage vow you took back then. Remember those words? "For better or worse, for rich or for poor, in sickness and in health?"
Remember, too, and this is very important, that love is NOT a feeling. Love is a choice. It is very natural for couples to go through phases where they feel like they do NOT love one another. When you act on those feelings, that's where problems arise. You're in that place now, where you do not feel the love you think you should have for your husband. You are vulnerable, and that's why you are experiencing feelings for your ex.
Love is a choice and a commitment. You made that commitment when you took your marriage vow.
Cheating is NOT the answer. That will cause more hurt and problems than you will know what do with. Besides, cheeating is only a temporary "solution" especially if this man is married. It's like putting a badn-aid on a wound that needs stitches.
Think of your ex's wife, and how this would make her feel. If you did get something going with him, it wouldn't last, and then you'd be right back where you started.
**The true problem is not with the person you are with, but with YOUR way of thinking.** Eventually, every relationship reaches the point where it feels stale, so if you seek a new relationship elsewhere, eventually, after the novelty wears off, you'll reach this same unhappy point.
You need to work through your problems, and seek marraige counseling. A very good book you should check out is "Divorce Busting."
Your ex is NOT the answer. Being true to your husband, and working through your problems (and it WILL be hard!) is the right thing to do. And the safe thing to do. If you stick to this positive way of thinking, in the end, you will be very happy with yourself for doing the right thing, and honoring your marriage vows.
A marriage is NOT simply a contract, it is the act of two people becoming one through the marriage. If divorce takes place, everything has been broken, and this is an abomination in God's eyes.
Don't take the easy way out!! Do the right thing! Get counseling! :)