1. For the Sake of Self-Respect
I have heard women legitimately argue that it is a display of true love to take back a man who consistently cheats on them. Wrong. It is a display of emotional dependency to the unhealthy level of justifying your acceptance of such abuse. If they love and respect you, they will not purposely do anything to lose you. People make mistakes, and if you are big enough to forgive the first cheating (I'm certainly not), have enough self-respect not to accept them back the next time they're unfaithful.
2. For the Sake of Pride
Too much pride can go awry, but just enough pride to counter your fear of abandonment may be healthier than not in this case. Many people return to unfaithful partners out of fear of change and abandonment. Let your pride be bigger than your fear and walk away.
3. For the Silence of Your Demons
There's a voice inside telling you that you deserve better. You desire to feel loved and respected and valued. That feeling, like you're just not quite happy with your love life even when everything seems "okay"... that feeling is that voice, and that voice is one of your demons. Sometimes the only way to silence them is by getting rid of what created them in the first place.
4. For the Sake of Self-Love
Loving yourself means taking care of your heart. And taking care of your heart means walking away from people who only break it. It's easier said that done, I know, especially when in the grasps of abuse and fear. But it is possible to escape; try to reflect on everything you'd rather be doing than being miserable. And whatever brings you a split moment of joy, leave and go with it!
5. For the Sake of Self-Preservation
Each day you stay in a bad relationship, you are allowing yourself to be chipped away bit by bit. It is exhausting, both mentally and emotionally, and it can take a toll on your love life in the future. The way you treat your next partner may highly depend on the misconstrued ideas developed from this bad relationship. Preserve whatever innocence to romantic partnership you may still have left and walk away.