Glad you clarified it some, Renee.
I'm with BFD on this:
she is afraid of being alone and would rather be miserable with your dad
It's a combination of human nature (wanting company with a mate) along with the JW mindset that you're not free until cheating/unfaithfulness occurs. Mom needs to widen her vision and see other options, or else she'll be muddling along for a long time.