I could really use some advice about my family situation

As-salamu alaykum, everyone. My parents have been married for 20 years. My father lives and works in another country, while my mother, my siblings, and I live here. Their relationship always seemed normal and strong, truly a blessing, until my father committed a major mistake. He engaged in inappropriate contact and exchanged explicit messages with a woman who is not his wife. My father is a practicing Muslim; he prays regularly, has performed Umrah, and has always cared deeply for us children. It feels like I don't know him anymore. My mother discovered this, and when confronted, my father complained that she doesn't make an effort in her appearance for him when he visits-astaghfirullah, I was there and I witness how she tries her absolute best to welcome him home in the best way. He even said she should wear makeup. My heart completely broke listening to this. My mother, a woman whose dignity and self-respect mean everything, stayed silent. She later came to me, asking if she needed to wear makeup or change something about herself. I was so shocked, I didn't know what to say. I tried to reassure her that she is beautiful as Allah created her and that she shouldn't let anyone make her feel otherwise. I'm so worried about what will happen to our family now, and I honestly don't know what the right thing to do is. My mother hasn't told anyone else, but I found out.