Hello I believe I can help you with your concern
I am sorry that you are having these recurrent fights with your girlfriend, I can imagine how much that stresses you.
I think your girlfriend is very sensitive and that is why it is easier for her to get in arguments and not get over things as quickly as you. This is not necessarily a bad thing, because it just shows that she cares about you and wants to things to be "perfect" in her eyes. But she is going to have to realize that not everything is perfect in the world and that when we do make mistakes we learn from it, that is how we get better.
Is your girlfriend considered very emotional or may be has been described as "someone who wears their emotions on their sleeves?"
So with her anger and frustration over this current argument about your friends watching a movie in you bed, she should definitely express her view point because it did upset you as well, but she should not have pushed it so much and caused an argument. Anger and frustration are natural emotions that should be expressed, but in a more assertive way and not in the way that she did. Assertiveness can promote change and actually help the situation. Here is a good worksheet that can show you what I mean about being assertive.
Anytime, my job is to help you as fast as I can
Your girlfriend may have an issue with emotion regulation and this is why she responds to certain situations in a very disproportionate way. So this means that what makes someone a little upset, would make her very upset, and this goes with all of the emotions too (usually the negative ones are effected the most). She actually is feeling this way, its just very magnified and that is what is causing her reactions that you are seeing.
This is not necessarily any type of diagnosable mental health disorder, but it can be helped with therapy if she is willing
I can also provide you with some techniques that can be beneficial for her as well during these moments
Well for therapy I recommend something called Dialectical Behavioral Therapy (DBT) they have a great model for helping individuals with emotional regulation issues. Many therapists can provide this type of therapy, just ask them if the are proficient in DBT. Also here is a good self-help link on DBT that can give you some more information as well
So her emotions are also being caused by negative thoughts, so if you stop the negative thought process you can lessen the impact of her emotions and behavior.
This link may help you, it contains a technique I use with patients called a thought record. It will help her keep track of any negative thoughts she has. She put the negative thought on paper, the emotion accompanying, the evidence to support it, and the evidence against it. Then I want her to come up with an alternative thought for the situation (more positive and plausible). This will help her change her way of thinking to be able to think more positive and not automatically go to a negative type of thinking.
The DBT therapy will help her with these selfish qualities as well. Her emotion regulation issues and with this only thinking about her self mentality can be treated well with therapy, but it takes time and a lot of effort on her part. Also she may be selfish because she thinks that a lot of people have hurt her in the past so she thinks she is the only one looking out for her, but in fact they have just acted normal, but she magnified it so much due to her emotional regulation issues.
Anytime, is there anything else I can do to assist you today?
Okay, well I want to wish you and your girlfriend the best of luck
If you have any other questions or concerns please feel free to contact me at anytime
I hope I provided you with excellent service today
You have a good rest of your day as well