Stay strong and embrace the life of freedom to come. Do NOT tell him you are leaving before you actually leave, this is our downfall. We always seem to think we owe it to people to be kind and explain things and it’s ‘the right thing to do’ blah, blah, blah. All that does is give them that chance to cry and plead and beg us to stay, promise us they’ll change, and then all the wind gets taken out of our sails and we then feel guilty if we were to get up and go.
My advice to you is to see your plans through and leave, then let him know afterwards if you must.
Good luck and best wishes.