I agree, leave them both and work on being independent before getting into another relationship. And never get involved with someone you work with, unless you don't care about your job and can afford to lose your job.
How old are you?
Your present marriage was begon on shaky ground, so it isn't any surprise that it is falling apart.
I don't think you should stay with either guy.
Do you have a problem with being alone? You're basically man-hopping without a break. You need to do some SERIOUS soul-searching about what is going on with you.
Definitely DON'T start anything with a co-worker. For starts, work is work, not a place to be looking for potential prospects to date. Secondly, if the relationship goes south and/or ends bitterly then you are faced with dealing with this man at work. Don't do that to yourself.
Whatever you are looking for isn't in a man.