I hate to burst your bubble, but you are not in love with this man.
You are in love with the idea of this man, and that is something very different indeed.
Because you are unhappy in your marriage, you are looking for an outlet for your unfulfilled needs, someone to give you back the feelings of excitement and fulfillment that you used to have, and you have lost along the way.
This man is obviously in blissful ignorance of your feelings, and you should kep it that way. Relationships in the workplace are frought with problems even when both parties feel the same way about each other - imagine if he was shocked and embarassed and simply didn;t reciprocate your feelings. He may feel he has to resign, report you for harassment, laugh out loud and tell al his friends - the scenarios are endless, and few of them pleasant.
What you need to do is recognise that this is a crush because you are lonely and bored, and this man gives you pleasure in a cerebral way, which is natural, and only harmful if it gets out of hand.
Why not try talking to your husband about ypur feelings - not about your collegue, but about your husband and you. If you get no-where, then try Relate who have vast experience, and could well set you both on the right track.
If, sadly, your marriage does come to an end, you will find love again, but don't put love where it does not exist just to make yourself feel better.
Hope this helps.