Yez, so glad to hear from you. It appears your Inner Warrior has finally emerged from the cave. That's a good thing, because gullible, naive, nice girls do not do well married to drug addicts.
No, you were not too harsh. I hope you achieve what you need tonight, whatever is for the highest good of your family.
There is no need to regret the valiant choice to give him another chance. He was working a recovery program, and you gave reunion a go.
It may have been too early to live together again, but only experience could tell you that.
As posted above, I think a legal separation with specific visitation guidelines is the best way to go. He needs to live elsewhere and your family needs the legal protections of a specific separation (or divorce) agreement.
I don't think anyone here needs to advise you about his manipulations or lies nor to warn you to expect the worst of him. If he's using again, as your gut is telling you, you know what happens.
The children.....your 6 year old boy, I remember he is the one most distressed by what has happened with his father's erratic presence and previous disappearances? Have you consulted with a professional about some counseling for your boy? He isn't too young. My son was seven when I left my AH years ago, and my boy received counseling. It's best for the child if he is helped by someone other than a family member, I think.
Whatever is to unfold, I hope you will always feel free to post here for support.
As far as grit goes, I think you've got that handled.