Stuck in a tough situation?

My fiance of 3 years and father of my child keeps getting caught within his own lies. Tries to deny it although i have the hard proof right in front of me. Be it cheating, lying bout things that i have asked him to quit doing repeatedly, and so on. Im stuck in the terrible decision i knew i should have made a long time ago before my beautiful daughter was born. I know i should leave for my own sanity and for my daughters safety. i love the guy but there is no trust in the relationship. i screwed up 3 years ago when we got together and got drunk and accidentally slept with someone and now he holds it over my head to this day to justify his false stories. he has lied to my parents, to our friends, to me, his own mother, everyone. to add on top of it he drinks daily and doesnt see a problem with it. am i just trying to stick out and see if it will get better or am i just letting my dignity go?