Stop mind reading. You have no idea what she is thinking.Hell maybe she doesn't even know.

Don't show those letters to her and don't let her find them. She will run for the hills. Plus right now whether you are going through hell or not is nothing to her. It will not influence her in your favour. If they help you, by all means keep writing them. It is a good way to release some pent up emotions.

Detaching is not easy. That is for sure but it is independent of being kind and validating. Reread the detachment threads. Being cold etc will not help you.

It is OK to tell her why. IMO. But yes consistency is the key

R 25 years
M 14 years
S11 & S13
Working on it alone since Oct 2014
M in trouble a lot earlier (~2 years)
Feb 2016. 1st R chat in a yr.
Next R chat Aug'17
Still together