I can understand how much it might be affecting you as you go through it so often.
When two individuals get into a lifelong bond like marriage, especially maybe without knowing each other well, a lot of things might come up where the difference in opinions, choices, expectations, disappointments, etc. and most importantly different stressors like securing future, managing finances, etc make them so much frustrated that they end up losing patience and fighting frequently. Another reason also can be because that is what they learnt from their parents and they do not know what other ways can be there to deal with their conflicts healthily.
But none of this is your fault, neither can you do something actually to solve it. There will be many such situations in life where we won't be able to solve them and it is completely okay. But if you really want to help, one very important thing will be communicating them how all this is affecting you and how you are impacted by it, deeply. And then together, maybe you can ask them to sit with you and decide how they are going to take care of it or work on it. Along with that, another thing you can also do is to suggest them for family or marital therapy or to just go for a few sessions with a Counsellor so that they can just talk about and learn how their issues and conflicts can be dealt in more peaceful ways as well.
And lastly, at times when you feel you are feeling extremely hurt or just want to vent out, you are always welcome to come for a session with the Counsellors here on this platform who will be happy to listen and help you deal with the pain.
Hope that helps!