It is common for anxiety to cause sleep disturbances. You may be successfully blocking out (by busying yourself with other tasks) bothersome thoughts during the day and at night, when you are less mentally occupied, they creep back in. That could explain the increase in anxiety right before bed.
Regarding your sister, you and she are close. You are worried about what would happen to her if you left. Have you and she discussed your college plans? What are her thoughts and feelings about it? Does she feel okay with it? Having this discussion may ease your mind.
Should you stay or should you go? Only you can answer this question. If I were able to speak to you in person, I would explore your reasons for moving away to college. Was attending college closer to home an option? If so, would it be healthy for you to stay? You wrote about how difficult it has been to hear your parents complain about each another. That’s a difficult situation to be part of and I can understand why you want to move.
Without knowing all of the details about your situation it is difficult to give you specific advice. Generally, you should do what is in your best interest. The reasons for going away to college should be valid. Valid reasons may include wanting to remove yourself from your difficult family situation or because of a particular education program that you are interested in.
Some people feel as though they “should” or “have” to move away for college because that is what they are “supposed” to do. Some say they would feel like a “failure” if they attended college near their home. These are examples of invalid reasons to move.
I would encourage you to do what is best for you and not what you think you “should” do. Talk to your sister about what she thinks. If you are not moving far perhaps you and she could arrange to meet periodically. Maybe she could visit you on campus. That might give her a chance to take a break from your parents. If that is not an option, consider other methods of communication such as webcam, Facebook, instant messaging, texting, and the like. There are many ways to stay in touch.
Remember, even if you decide to move your plans are not set in stone. You can always change your mind and move back home.