It begins for its own reasons for each one of us here who have left....... but the common thread seems to be that it just doesn't seem right. It sometimes begins as a gut feeling that there is an insincerity of oneself to stay, and the honest thing to do is to leave.
I had that very similair calm "you know its right to leave" kinda moment but it takes the biggest balls possible to actually do it. It def takes strength and character to pull it off and remain intact, and yes therapy with a professional really makes a huge impact on leaving as a whole person.
I sometimes still shake my head and can't really believe that I am free now! That is motivation for me to never look back.
Good Luck! Yeah U need that too! no matter what they tell U.