Oh, Puppy. I sooo know how your wife is feeling. Her letter to you was very well stated. She is looking to you to be a team in fighting for your marriage. She is sharing her fears and feelings of apprehension with you. This is not the time to call bullchit. She is reaching out to you to understand her and listen to her and share your feelings. Validate her feelings. There are no wrong feelings, but make sure to reassure her of your love and commitment and hope. Tell her how THIS time will be different and specifically tell her why and how. You may need to really think about what you are going to follow through with this time (mainly counseling, consistent relationship talks, dialoguing if need be, etc.)
My suggestion: (I'll write a sample letter. It's easier for me that way)
Wife,
First of all I want to tell you that I love you and always will. (Insert your feelings about your wife and how that will never change).
I believe that I have found out what love and commitment truly mean. There is no relationship that will never come upon "hard times". Relationships that last are the ones that have couples that work at it all the time. That don't give up. If we wanted to be with someone that met our every need every second without much effort, we would be changing partners weekly. We change as human beings as we get older, but unless we want to change partners every year, we need to work with each other to grow together. Sometimes this will mean that we will disagree about things and have to talk it through. Sometimes this may mean that we have to see a counselor because the issue is too big for us to handle. Sometimes this may mean that we won't have that new relationship feeling you can get at the beginning. I believe long lasting love is better than new, temporary love. The "It" that keeps happening may just be what happens when you are in a long relationship. We just need to find what we can do to change the dynamic or at least understand it. We need to put forth the EFFORT always and forever. This won't be an easy thing and it won't be something we do and then it is done. I believe marriage is something that you need to constantly work at.
I see what your counselor was saying. I'm sure he/she has dealt with many couples that try to bury all of their problems under some romantic distraction. I do think we are different. Telling our boys that we have problems and that we are going to work them out is a good way to put it. It's a good thing to teach them that marriages take effort to succeed. The renewing of our vows may mean something different to the counselor if she/he is not a religious person. Our vows state specific things that we believe: I promise to be true to you in good times and in bad....love you and honor you all the days of my life.... To me, that's not a romantic/wishy washy emotional thing per se, but a commitment of my love to you period.
I know what you mean about feeling relief and also about feeling fear. Yes, we have been through this "trying" before, and ended up where we were both unhappy. I believe this time is different. I won't stop loving you. I won't ever want to leave you. I want to be with you for the rest of my life. I won't give up on you, and knowing you won't give up on me, takes us to a new level. We haven't ever gone to a counselor before to work on specific issues. This will help us. It won't be easy, but I know that we will get through this. Actually, I look at other couples that have never gone through really difficult times, and I honestly feel a little sorry for them. It isn't until you can get through the hardest of times with your spouse, that you can truly look at them with unconditional, not taken for granted, pure love. I feel like we will move to a level that not all couples ever get to.
All I know is that I love you. With that love, and with God, EVERYTHING is possible.