Tonight my dad and I were talking about various things, and the subject turned to my relationship with my mom. I confessed that I am concerned things will never get better. He told me that I may be wrong about that, because she seems to be putting in an effort to change.
(I never told him that she confided in me about their marital problems, but he finally told me his side of the story)
Supposedly, she was the first one to bring up divorce, and was hoping that he would say "no, don't go", like he did when they were younger. To her dismay, he just said "okay let's do it". He admitted his approach was cold and harsh, but he thinks it got the point across. He was never planning to leave her, but he was exhausted with the current state of their relationship, and he would not miss her or try to stop her if she tried to leave him. I think she realized that she can either cling to her selfish behaviors and leave him, or try to become a better wife and grow old with him.
Ever since that night, he has noticed a positive change in my mom. She hasn't really changed any of her well-established bad habits, but she has become conscious of them and recognized that they are wrong and hurtful. She will often approach him gently and humbly after an 'episode' and apologize for her actions, which is something she's never done before. She also seems to be coming to terms with the fact that she can't be in control of everyone's life. My dad's point was that she is trying, and he has hope that things will get better. He has the same hope for her relationship with me.
They have 3 sessions scheduled with a christian counselor in the next few weeks before they leave on their mission trip to the Philippines. Hearing my dad's recent observations gave me a lot of hope.