So. . .if a person's actions speak over time. . .how long does it take to know for sure if somebody is safe?

One person i trusted was very good to me for 5 years and then suddenly abandoned me in a fit of rage. It was so unexpected and feeled like it would kill me!!!!!! How come i didn't know before then???? Was i missing something???? Does it take YEARS to know if someone is safe???

Also. . .Most people are not willing to wait years for a person to learn to trust them. T's are different in that regard.

Are there ways to know earlier if a person is safe???