You are making an error in logic when you start a statement with "She feels . . . " You cannot directly know how another human "feels." You can hear what others say and observe their demeanor and their way of interacting. What you are able to take in are another person's statements, and you can observe another person's "affect." Affect is what one person can directly observe in another person's demeanor. Affect can be described as angry, enthusiastic, sad, confused, etc. All these adjectives describe a person's inner state of mind, which is never directly observable. Humans are constantly forming "theories" about what other humans are thinking. It is necessary and important that we do that. But it is very important that we distinguish between what we know firsthand and what we believe based on "theory." You're a bright person and you can easily understand that. However you are still young and very much under parental influence. When you start off a statement about your mother by saying "She feels . . . ," you are stating as fact something that is really just your theory. You may be right, or you may be wrong. You can't know what anyone else "feels," even your mother. Even if your theory is based on your mom saying, "I feel this or that way." Humans are notorious for misreporting how they "feel," even to themselves. This is naive of you.

The longer I've lived, the more I've learned that I can misread the feelings of people, even of close family members. People censor their expression of feeling to express only feelings that they trust will be acceptable to others. Your mother has mixed feelings about your father. Years of marriage lead to complicated layers of feeling. You are deluded, if you think you can know what your mother holds in her mind and heart. It is more complicated than you have any idea of. Of course, you have to formulate theories. That is necessary to interaction. Just don't overly rely on them. Also, be aware that humans try very hard to control the theory that another human has of the first human's thought processes. This is part of how humans manipulate each other, and we all do it. To some extent, it's even constructive. It helps preserve the peace. In curtailing the behavior of a toddler, a parent will sometimes pretend to feel more anger than is actually the case. This is to have an intended impact. You seem to not be fully aware of how much guessing you are doing.

Another telltale sign of someone being at least a little confused is to start off a statement with "We feel . . . " You sound like your mother and you share a joint-mind. And 14 year old sister is also supposed to participate in this "group think." Humans can't engage in "collective" thinking. Each individual does it individually. There may be impressions held in common. But I promise you that your mom has at least a few thoughts about your father that would surprise you.

Parents are naturally sensitive to how they are viewed by their children. When there is conflict between two parents, it is natural for each parent to want to be seen as "the good one." Parents can be quite strategic about what they share with their kids. You describe your mom as "controlling." Don't think she is not wanting to control the "theory" you have about her marriage.

I'm not seriously recommending that you refuse to listen to your mother venting. But concentrate on "listening." Be less eager to endorse your mother's take on things. Be less eager to co-plan your mom's future with her. If your dad was hollering loudly at your mom, you can honestly affirm that "Dad sure got loud yesterday." But what your mom should do about it is really on her. You can advise her that she needs to do "what she thinks best." But this is not something for you, sis and mom to have a vote on. If your mom needs to be listened to, it's okay for you to say 'I hear what you're saying, Mom." That's a far cry from you saying, "I think Dad and you will both be better off, if you separate." That you do not know.

It may be appropriate for your mom to get out of this marriage. She might have a better life, apart from this man. That's for her to decide. There are risks to that, especially in the way divorce would affect your dad. It is very likely that losing his marriage will not spur him on to a higher level of independent functioning. More likely, IMHO, he will further decompensate and get himself into a downward spiraling mess. That doesn't mean your mom is obligated to sacrifice her future on the altar of saving Dad from himself. But let go of wanting to put this happy, hopeful face on things whereby divorce will be a win-win for all concerned. The outcome for your father may be sad, and no small burden on you and sis down the line. Mom foresees more of what can go wrong than you do.

I'm not big on recommending therapy to any of you. I don't think it would change much. Mainly I recommend that you patiently leave your parents to work out for themselves where they each go from here. Don't get caught up in "group-think." You are daughter to each if these individuals. Concentrate on managing those two relationships, which are yours to manage. Don't get set up to bear the burden of consequences that your parents will face for not having built a healthy marriage. If Mom separates from Dad, that will be all the more that she will invest in controlling you. You already show striking signs of not knowing where she ends and you begin. This has tremendous potential for undermining your future relationship with a significant other. Then you'll be posting to a thread that starts off, "I'm having some issues with my boyfriend, and my mom and I think/feel that . . . " Not the direction you want to go in.