ohh how did i get into this mess? What shoud i do?

Well, Ive been married for only 3 years and we have been separated for about 4 months now... We separated because we had a huge argument. Basically i saw a bunch of things that were not right in our marriage, and she failed to see that there was any problem!

She was Co-dependant.. always had to be involved in everything i did and would not allow me to go out on my own without getting angry with me. She was way to dependant on me to pay the bills and take care of ANYTHING within the marriage that required responsibility. She could not have fun without me and would NEVER go out on her own with friends. She was Jealous of almost ANY girl that i even talked too and became almost obsessive about visiting me at work in my previous Job. Our other issues were a little more personal, she had some psychological issues and medical issues that made intercoarse difficult and in the end i simply couldnt be bothered anymore. Its not like i didnt try, I encouraged her to get counselling and see a doctor many times... She said she would do it, but never did.

She has also twice stood in front of the door to stop me leaving during an argument, and this still plays on my mind today... I needed to get space to calm down, and she stood there and refused to move, and also told me that im not allowed to touch her or she would call the police on me (not that i would anyway)...

So I left, been living at my parents for a few months. She recognised her bad behaviours and this time has finally decided to do something about it. I see that she has changed and is working on stuff, but is it too little too late?

During the last couple of months I have met a nice girl at work, whom i feel i get along with soooo well... You know some people you just click with, well this is one of those occasions. Not only that, but she is interested in something more  between us. We started seeing each other alot and things developed quite quickly... We slept together, and then i realised that what i was doing wasnt fair on her so i backed off.. and tried desperatly to put rules in place so that sort of thing doesnt happen again, at least until im in a better place perhaps down the track.

A few weeks later i still feel strongly for this other girl, but my wife has worked on her stuff and is changing alot...

So what should I do? My wife is begging me to let her have one more chance so she can 'do things right', but i have never got along that well with her, and im actually very interested in this other person whom i feel i could be very happy with, but making that final decision to not go back to your marriage is a very hard decision to make and i still feel like something is holding me back. Is this normal?  Has anyone gone through a divorce but found it really hard to take that first step?, or should it not be that hard, and do i need to try again with my wife?

Perhaps to add info to this situation, Yes I have attended counselling with her, and have done personal counselling also. Im also not just jumping from one person to another, I have waited a few months as i did not want to be the sort of person who jumps into things in a 'rebound' type situation.... I have tried very hard to back off from the co-worker, but this is very difficult as I see her 5 days a week at work.