How would you feel if your wife met another man? Felt this spark with him and not you. Perhaps she should play the field and test drive another man to see if this would make her life more content. Maybe she should be the one starting an affair with someone new.
Work on your marriage. Get your spark back or create a new one. It's not that difficult. It starts out with a few compliments to your spouse. Stop carrying around your resentments towards her.
If you are not willing to fix your marriage, take the easy road and divorce her before you even speak to this other woman. BTW, you are in the midst of an emotional affair. You already are "cheating" on your wife, emotionally.
There are no excuses that can justify an affair. It would not be your wife's fault, but the fault of your own actions and betrayal towards her.