A coworker who I've known for 2 years and I hit it off from the beginning. We work closely together on projects so spend a lot of time together and have gotten to know each other really well.
Holy Cow! You decribed me flash forward for you about 3 years! Here's what I advise based on my personal and ongoing experience - DROP THE THOUGHT FAST!
Unless you're looking for a whole lot of excitement, stress, anxioty, sleepless nights, pain, hurt, trouble, etc. etc., you need to FIRST get it figured out with your wife without the distraction of someone else being there to cloud your vision. You only have the following list of people who could potentially get emotionally hurt unless you take care of matters outside said distraction; yourself, your wife, your daughter, the other woman, your family, your wife's family, your friends, your wife's friends, the other woman's family and friends, your coworkers, people you don't even care about who are your neighbors, and on and on. Just think about the concept of trust and how hard it is to keep it, but how easy it is to lose it forever. It only takes once. I'm telling you - you're playing with fire here. You WILL get burned if you aren't smart.
On the other hand, you could do what I did and get involved (emotionally) thinking that you can handle it - that you're justified because of blah blah blah about your wife not meeting your needs - that you can just do what you think you need for yourself becasue of blah blah blah reasons and you only have one life to live so you might as well make the best of it - that love will trimuph....
Well, if any of that rant is even close to what you've been telling yourself, you're already in over your head.
If you haven't said anything or made a move yet - your lucky - don't. At least not until you're legit and have finished EVERYTHING with your wife (that's a whole 'nother' rant).
All this is coming to you courtesy of my personal experience - because right now, I'm standing in front of a 90 mph emotional freight train - it hasn't hit yet, but it's coming. I hope my rant can spare you pain similar to mine - just don't do it - at least not until you know you've done the right thing about your current relationships.