It was not wise of your mother to share information with you that is painful for you and that you can do nothing about. But what is done is done. I suspect that your dad is well aware that your mom is distancing herself from him.
This is a matter between your parents. Although you may want your parents to get counseling, you can’t make it happen. If your dad wants to keep the marriage, he needs to face the problems. It might be helpful for him to get into counseling and then to urge your mom to join him.
It’s important for you to remember that parents who can’t find a way to get along with each other can still have solid and loving relationships with their kids. Focus on your relationship with each of them separately. At 18, you are about to launch your own adult life. Although it complicates things, you don’t need your parents to be sharing a household to be close to each of them.
I wish you well.