A few things :
- you simply cannot force your wife to do anything, or be anything to you...that is, coping begins not with what she does, but with you; and
- there are numerous ways of coping, and better coping mechanisms are about that - finding better coping mechanisms for yourself; and
- to find better coping mechanisms, you need to focus on who you are : what you find enjoyable, what you find stress relieving, what you are passionate about (other than your wife), what you find fascinating, what work or exercise wears you out (physical activity is one of the great antidepressants of all time); and
- being outdoors (the sun is also a great anti-depressant), talking about it, being around friends, patting a pet are all part of an effective plan to remind yourself of the things you enjoy in life (other than your wife).
Next, it seems you need a little perspective. Your wife hasn't even met this man, has she? So she hasn't slept with him? You are then, in a much better position to save your marriage then if it had gone any further...
Is your wife unhappy, or bored, or is she the type to take advantage of circumstances?
The first two you can do something about. Doing something, without expecting results, starts giving power back to yourself (not from the relationship, but from within - and internal power, otherwise known as self belief and self esteem, are necessary to coping). The reason you don't expect results is because, again - you can't control the other person. You do what you do knowing the reasons you do it (for love) are valid and meaningful...and you see if she comes to the party...but if not - you did it because you have a heart of love, understand? If you value a loving heart, you value the 'you' who did this without reservation, yes?
Lastly, as a word of advice - in almost all failed marriages, the guy stopped chasing first. If you think about it, guys build the house, and women furnish it...marriages are the same. If the guy stops building (chasing), the woman eventually stops furnishing.
...of course you do have to recognise when you keep building, and no new furnishings are added - but that' doesn't change the principle.
If you by chance still find that hard to grasp, then ask yourself 'what makes my wife feel desired?" If she doesn't feel desired, what will that result in?
Think about it