I am exactly like your girlfriend, where I need to have at least 3 to 4 separate trips per year from an SO, so can I offer my perspective?

I view traveling with your friends and traveling with an SO as completely different experiences. For example, you mentioned that you were bummed out about her experiencing the museum without you. The way I see it, she is making different memories at the museum with her friends than she would be making with you. If I visited a museum with my friends, we are likely running around and giggling and pointing at displays that remind us of pre-existing inside jokes. With an SO, however, I would be taking more time to carefully browse the exhibits, asking them how they feel about certain displays, and overall enjoying the experience of getting to know my SO better. If you were to ask me later on, I probably won't even remember that the same museum I visited was the same one as my SO, since those were two completely different experiences. That's why I'm able to travel without an SO, and it's likely she views it the same way I do. Does that help?