I have been married 24 years, husband filed for divorce. He is now dating someone else. Are we still considered legally married?

You are legally married until a court grants the divorce. Simply filing doesn't end the marriage.

However, that doesn't mean he can't start dating again. You can too if you want.

Agree with Scott, I am not sure of where you are trying to go with the question, many men or women start dating before they even file for divorce, or heck before they even separate.

But yes you are still legally married, but it is not uncommon for people to date at this point.