Don't do anything. If you do, you will regret it at some point. If you do and you end up staying with your dh, you will feel guilt for a long time.
If you are not sure how you feel about your dh, then that is another issue to address. Do not use your feelings for this colleague as a way to test your feelings for your dh.
Having this chat was not wrong, after all, it is OK to window shop, as long as you don't buy the goods. If you still love your dh, go no further. Remember, any action you take will affect your ds, and this man's children for the rest of their lives.
Re the work situation, flirting is fun, as it boosts self esteem, and reminds you that other people see you as a woman rather than a wife and mother. BUT, if you think that flirting with this man could be dangerous, take a step back, and just be friendly with him when you have to talk. After a few days, things will hopefully go back to normal. Try to be professional in the office, otherwise other people will notice your mutual attraction. Remember, you are there to work!!!