Maybe you're not having an affair, but this is much worse.
How Would Marla Feel?
Whether or not you want to label it "an affair", you're doing as much or more damage by seeing Marla (and telling your wife about it) than if you were having the tradition type of affair. Think of how painful it would be for YOU if Marla went off to "talk" to some other guy all of the time. That is what your wife feels. She knows that you are emotionally unfaithful.
Why Did You Miss Your Opportunity?
What worries me most is that you had an opportunity to be with Marla before you got married and you didn't take it. What's up with that? Why has the urge to merge struck you now?
Leave Your Wife AND Marla
Yes, I think you should leave your wife. (Your family isn't married to her -- you are.) I also think you should leave Marla. Then, before you get involved with anyone else, you need to get counseling. Otherwise, you might just end up finding someone else who interests you while you're in a new relationship.