Am I the "villain"?

Hi everyone, 

I apologise fo the long thread, but there are some things I need to get off my chest. I have an ongoing situation with my parents and I am beginning to lose all my strength and hope. I do not exspect any advice or guidance (though much appreciated), I just need to write my worries down. 

I am a 33 year old female and for most of my life, I have helped my parents with their relationship/marriage. My dad remarried something about 15 years ago. He and my stepmum have to sons, my younger brothers. Since I can remember I helped them in daily life, supporting them however I could. I would bring them to kindergarten, to after school activities, to school and so on. 

Sadly, my parents are not getting along well. They never really have and I think they are not a good match for each other. However, I also understand, why they did not want to seperate because of the kids. 

For a couple of years now, their whole relationship worsened. They scream at each other almost everyday: for small things, for medium things, for big things. So just in general, whenever they see each other, the start complaining about each other. Saying bad things about each other, in front of the kids, in front of each other. It appears that there is not a single thing, they find attractive or appealing in the other person. 

They talked about divorce but never go through with it in the end. 

So now, both of them started to gain my support for their cause. Whenever they fight, they want me to take their sides. My dad is complaining that I do not say anything against my stepmum, and my stepmum complains that I am not with her side. 

Basically, they both want me to say to the other person, that he/she is wrong. 

With each fight (so with each fight), it gets worse. They are telling me to my face, that I am a coward for not saying anything bad about the other person. That I should take their side and defend them. Especially my stepmum wants me to protect her, because she says, she cannot do anything. 

To be honest, I dont want to be involved in their problems. I am and always be a mediator. 

Unfortunately, my help in their daily life has gotten so essential, that without me being there, they would not be able to work their professions. So I am almost everday at my parents place, e.g. when I am picking up my brother from school, bringing him to his activities and what so not. 

In younger years I used to be more resilient, but now I feel that I really got weak and I cannot stand them fighting. My chest starts to tighten and I feel very unwell. 

Thanks for reading and everyone have a nice evening!