I started dating fairly quick after I left my ex husband. I had know the guy for 12 or so years previous. I was very comfortable with him and at the time, it just felt right. I learned after the fact that might not have been the best move. Like you, I was mentally out of my marriage long before it was actually over. I was very young when I got together with my exhusband and i never knew what it was like to "date" someone. I fell in with this other man but I think it was because I was afraid of being alone.
With that being said... DATING SUCKS and I am not very good at it. I do not know how to do it right. I have had a few BF's since my divorce in 2007. Nothing signifigant by any means. It is a big game and I have gotten really good at figuring it out.
If it has been awhile since you have dated.... be prepared a lot has changed. GOOD LUCK!!!!!!