"A week after this she confided in me that she didn’t have intentions to come back from that walk, implying she was going to kill herself."

This incident alone is reason enough to cut ties and run

This is either a suicidal individual, or a deeply manipulative prick (no matter what sex, gender etc.).

If a) even when a close family member, beloved partner or long-time friend pulls something like this, they need professional help urgently which cannot be provided by their partner/friend/relative.

If b) please practice self-care and walk away, you don't owe them anything.