12 years of living with addicts is a long, long time.
Tough love means getting tough with ourselves- creating boundaries to protect ourselves and enforcing them.
An example of a boundary is "I will not live with anyone in active addiction."
A boundary does not seek to control the behaviors of other people because they are free to live their lives as they see fit.
If you want to write an impact letter, do so for yourself and reread it as often as necessary, to maintain your own boundaries.