How to deal with the guilt of leaving

Once again I've caught my husband lying.  His addictive behavior and lies have destroyed our marriage.  I'm tired of the same song and dance.  He is only remorseful when he is caught.  I can't continue to live in fear of what my husband is doing and know I can't trust him.  I am seriously considering moving out.  My husband works long hours and if I move out, he will see our son even less than he does now.  In a way I feel this could be good, because as soon as I leave, he will drown his sorrows in booze and destructive behavior.  I am feeling guilty knowing that I will be changing my son's life forever.  Once I leave, I am never coming back.  Yet, I don't know what more to do.  It's been years and years of dealing with his destructive behavior.  I've turned into his mother trying to control him and keep him from harming himself, our son and me.  I can't do this anymore.  Yet, I'm not sure how I'm gonna live with the guilt.  I hate this.