And that irony now is that messenger on Android is RCS compliant and currently has this exact functionality, except it’s less trustworthy.
Once again I’m using one messenger and everyone else who’s using an RCS messenger gets encrypted, but SMS (clearly marked as such) is a viable fallback.
Your story is very sad, and I am sorry you had do go through all of that. It sounds pretty horrific and over an extended period.
I hope you find some peace, through talking or posting or maybe eventually some therapy.
I think you will find that more people are supportive than not, though every crowd will have some assholes. Be selective with irl folks that you talk with, but finding a support group could be very helpful.