Think this is a pretty common cycle in an unhealthy relationship.
One person is unreasonable (over critical / agressive / drunk / negative - delete or not as appropriate). Acts oblivious to it because it's become the norm not to be challenged.
The other feels hamstrung and unable to clearly say what they feel because of fear of more criticism / agression, etc (with validity). That leads to passive agression / sulking / crticism in safe environment in front of others, etc.
The unreasonable partner then, on some level, knows that the other is unhappy but carries on with the totally misplaced justification that sulking, etc is not fair - they should say what's up if they're unhappy - so being frustrated is ok.
The hamstrung partner then feels even more hamstrung and gets even more upset / scared / trapped / helpless.
Continue ad nauseum until it becomes unbearable for one or the other (or probably both) - then mix in the practical and emotional head scramble of 2 people who used to love each other splitting up and neither being in the wrong and BOTH being the victim with lots at stake.
Presumably at some stage at the beginning of the relationship it wasn't that way so the cycle will have developed slowly over time and become ingrained. Imo that's what makes it so difficult to get out of. At some time presumably the communication was good / unthreatening / both partners wanted to make the other happy by listening and acting.
Are both responsible? Probably, but the unreasonable partner is, I think, commonly "more responsible" - in that cycle it feels like as time goes on the unreasonable partner feels like the one who has damaged the means of communication more.
But imo very wise thing to say "But mum also has to do less being wronged and more positive action-taking. And she won't."