break ups.

how do you know its time too let someone go but for good...? what made u realize that person wasnt the one for you?. I dont care which ever question u answer I just need something answered please. I know everyone/relationship is different . I know it also depends what the situation is about. but besides all of that what made you leave and never look back. I need help not urgent help but the help that can guide me in a way . I feel my relationship isnt what I thought it was.