Tjp, my heart and love is with you. I remember the feelings you describe so vividly. I tried to keep myself together with others but the moment I was alone, I drowned in sadness and cried and cried and cried.
What helped me immensely was to realise that my children are on their own paths. They have lessons they need to learn and I cannot and shouldn't interfere anymore. I cannot make them walk the path I believe they should. God knows I tried for many years and was unsuccessful every single day.
There is an excellent 11-part series on addiction on YouTube. The first one can be found here:
The Truth Behind Addiction 1/11 - Byron Katie - YouTube It is by a woman named Byron Katie who gives a very different but helpful perspective on addiction. Maybe it will help somewhat.
You are not a bad mother. You did the very best you knew how. You CAN give yourself permission to be happy even when your children are not. You owe it to yourself.