Have you tried councilling? 20 years is hard to break but your not happy, your cheating and lying. You asking this question in the 1st place is a sign that it it should probaly be ended but I really recommend couples therapy 1st.
Now, i know about this stuff, am going thru it now and i married for nearly 20 long years unhappy many many years, i have 2 dependant children, and god i am getting out. he cheated 5 yrs ago twice almost a third and i can't wait to be living my own life away from him. I take totally what bliss407 is saying and know EXACTLY WHAT SHE MEANS. I have yet to meet my MR LEO (starsign!) I refuse to look back, loads of it is misery. I will look forward to being happy, and as each day goes i'm getting more independant, baby steps, but i'm doing it !
I am doing this for myself and my girls, i don't want them growing up thinking it's ok for a male (i won't call him a man - he's not) to be abusive and controlling.
My advice if you can't improve on what you have and know it's REALLY OVER then go for it, find your new life as i will do and do not look back. just be sure IT'S OVER.
Confusedandisolated, you don't need to be, just figure out what YOU WANT. Good Luck
Love Wish x
P.s. bliss407 gave excellent advice, it's that kind that helps to motivate.