This kind of problem is exactly why it's not always a good idea to date people you work with. It sounds like there is a lot of insecurity coming from your GF surrounding your relationship. When she says things like, "you never want to spend time with me", it sounds like she is picking up on some of your frustrated energy. Notice how she says, "you never want to spend time with me", and not "we never see each other." There is a big difference in those statements, and it sounds like she notices that you are frustrated with the amount of time you spend together. I think the issue isn't necessarily that you are together too often, but that you aren't getting enough time for yourself to be alone. It is clear that you care about her and that you want to fix this issue, so there are some things you can do.
The number one thing you need to do is tell her how you feel. In your OP, you said this: "I try to see her as much as i can, but i feel i have no more free time on my hands.", and then you go on to talk about the trip you are taking together and you say this, "i want her to come with me because i like having her next to me, i like her company." I think it's important for her to hear that you ENJOY spending time with her. If you are grumbly or anxious around her when you are together, she most likely can feel that. I do think you need to explain to her how important it is for you to get enough time to yourself, though. Say it exactly the way you did here, that you enjoy spending time with her and you see her as much as possible, but that it's important to your overall health and well being that you have some time to yourself as well. If you reiterate how much you care about her and how much you enjoy spending time together, it may make it easier for her to accept your need for alone time.
Unless you two talk about this, you won't get past it. Talk about how you feel and ask her how she feels. Both of you need to communicate what your needs and expectations are, and then you both need to listen to each other and respect the needs of the other person.
"Caring is not an advantage."