How to approach girlfriend about having a day or two to myself and friends?

First of all, how are you being selfish? You're just trying to be a good boyfriend. The thing is you need to tell her casually "look i love you but i want to go on this trip and i won't be able to text you too often but I will update you three times that day." It's reasonable. But honestly, I think you also need to confront her. Maybe start with that and also tell her calmly that you are asking for a compromise. Maybe have a friend of hers back you up or something as well. I noticed an ex of my best friend would often come to me for advice and I'd talk to her sometimes to tell her his side and it worked. And you can't be afraid to fight in a relationship. She's not right all the time or anything. Tell her that it's not good to contact so much in a relationship. Maybe even go to a neutral person together (doesn't have to be therapy even just a mutual friend) and see what they say (they will agree with you most likely as long as you're nice and calm about it which seems like you).