How can I support my dad in his divorce?

I’m mid twenty and my dad is end fifty. The relationship of my parents is super messed up since I can remember. Also I did not have the best childhood, I have CPTSD and I’m doing trauma therapy rn. My dad prob has CPTSD too, like his childhood was absolutely horrific (fr like imagine regularly seeing human corpses as a child, friends dying in front of his eyes, horrible parents and much more). My mom is a manipulative b who socially isolated him from his family, his friends and basically everyone else. She’s blaming him for literally everything (like completely made up bs) and always has to be the victim and does EVERYTHING to be portrayed as that. So the thing is, my dad really really loved my mom. Like fr. Last year, he told me he could never imagine being without her Blabla bla. But. Two days ago we met (I broke contact with her, he’s supporting me and I love him so much) and he told me, that in the last half a year he felt like his love for her is fading away. He cried. It’s hurting him, to feel how less she matters to him day by day. And he’s completely alone, he doesn’t have long until retirement. That’s why he’s talking with his daughter about it. I’m literally the only one he can talk about this with. And I really wanna be there for him. I see that he NEEDS TO DIVORCE. Like really. Otherwise idk how tf he thinks his retirement might look like. But also I’m his daughter. Who also has a messed up relationship with his wife/ my mother. I really don’t want to make my problems to his problems and that’s what I’m scared of. I want him to make this decision for his sake. For his happiness. I don’t want to interfere in his decision, manipulate him or anything. I just want to be there for him. Support him. BUT idk how to do that in a healthy way? Like maybe ppl who did divorce, what did you need from your children? How can I support him best?