I have been on the receiving end of this, and in the end the "great love" my husband thought he had ended in less than a year once life's responsibilities and stresses came in to play. He now lives with serious regrets because I wouldn't take him back.

My advice to you is to take this coworker out of the equation completely for now because you can't make any objective decisions about your future with him waiting in the wings. Seek some personal counselling (and possibly marriage counselling) to see if your issues with your marriage can be resolved and do some soul searching to figure out if you are still in love with your husband.

If you still don't want to be in the marriage then end it, not because of another man but because you don't want to be married to your husband any longer. Make a clean break from your current marriage and take some time for yourself before making any commitments to another man. If you are meant to be with this other man, it will all work out for the two of you in the end, no matter how long it takes.

On a final note, whether you realize it or not, you are already having an affair. An emotional affair is just as serious and damaging as a physical affair.