my mom cheated on my dad who has pancreatic cancer. i recently discovered her instagram threads account under a fake name where she rants about how my father isn’t good enough to her, and how she longs for a man she cheated on him with. not to mention the texts between her and multiple different men describing the sexual encounters they shared together. my mother believes my dad is not caring enough, and isn’t good enough in bed, ignoring he has a life threatening cancer. my sister also knows about the affairs, in fact, she was the one who told me, but she has said that i absolutely cannot tell my dad or my mom what i know, or else she will kill herself. i want to tell my dad so badly, so he doesn’t have to spend the time he has left with someone who doesn’t love him, but i don’t want my sister to take her life. i have the feeling my mom is just biding her time until my father passes away, so she can keep his money (he is much richer than her) and go fuck whoever she wants.