don´t trust much in the things and persons

All the things can change in one moment, for example, in a relation, two persons folling in love, can be one day very happy inter they, and other day can be very bad between us and broke their relation only because the two persons had a bad day, ans the rest of they life they will can  repent of their acts in the past.

I want to say this, that never believe that things are forever, because in one day, the things can change, and be very different, don´t trust much in the things and persons.