Anytime, people start being super-nice and out of character, I question intent. It's suspect, to say the least.
I have often said, it's better to be alone, than with someone who mistreats us, which leaves a feeling of loneliness that supersedes just being alone.
Sorry for your losses and heartbreaks. Is your grandchild, now a part of your daily life? Can always find solace in grandchildren.
Have you ever tried alanon or other similar support groups? How's your religious social circle, are there supportive people around you, to be there for you, through all of this?
Heroin, is quite the drug; do you know, if your children started with prescription pills? Perhaps, dipping into your stbxh's stash? There's usually a beginning, before reaching out for that particular drug. I've known of a few people that became addicted, my dad's youngest brother is now incarcerated for the rest of his life, due to his struggles with heroin. Deep down, it's a better place for him. He actually made, the state news, as a media story, a couple years back. My dad, had called and told me, to watch for it.