A quote cleverly echoed by Norman Cousins throbs in my head during those seldom, heartbreaking times of loss: "Death is not the greatest loss in life. The greatest loss is what dies inside us while we live."
From previous questions you have posted, I know that your girlfriend suffered from a rare form of blood cancer, and having had a close family friend who also lost her life from a similar condition, I can feel your wounds and the emptiness that seems permanently etched inside. Whenever I felt the hurt hurl an endless stream of bullets at me, I found solace only in sleep at night, and the words in the pages of books, but sometimes, the nightmares and the stories felt like nothing but putting a Band-Aid over an already-inflamed wound: It could only act as cover-up. The blood could soak through, and all efforts to terminate the lifeless thoughts were futile.
In the grand scheme of things now, I can imagine how bleak things are looking. Death casts such a degrading spell on us. You feel your spirit weaken and your knees crumble beneath you. Having these feelings are definitely normal, but it will be so harmful if you keep them inside and let the hurt bottle up within you. Since I don't live in US/Canada, I'm not quite sure what might be offered overseas, but I am aware that there are self-help programs that teach how to cope with loss. At the very least, there are sections dedicated to this in bookstores, and even reading a brief passage on coping, what to expect, and how to deal with it will benefit you greatly.
While your girlfriend's memory will permanently live within you, there are ways you can look back and recall the happier, livelier memories as opposed to the sadder ones. I remember you posting a question about 2 months ago to which Skylark answered beautifully. I'm absolutely positive that you did everything in your ability to make those last period of time immensely happy and heartwarming for her. Look back to that time when you painted her toes, watched a beautiful film together, or wrote her love letters. Poems are incredibly cathartic to me, so I will post a few below. I absolutely love "I carry you in my heart" by ee cummings. Let your mind drift back to that day where you held her hand and felt complete, and the love wash over like a refreshing wave. Let the nostalgia sink in completely, and embrace it like a hug, but don't let remorse or sadness stop you from feeling the bliss. Every day, devote at least 10 minutes to sit in solitude while overlooking a beautiful sunset or summer storm, and you will feel at peace.
College is supposed to be one of the most incredible four years of your life, so you deserve to feel lighthearted and to live life to the absolute fullest. When spending time with other people, let yourself go. Let go of the inner grief that might stop you from being your highest potential. Laugh often, and soak the in the splendor of the moment. Nature is a blessing to me, so every once in a while, I just like to relax and let the wind be a soundtrack to my day. When you're by yourself, it's easy to let your hair down and it's obviously harder to distract yourself from thinking about her. Think of it this way: The more you convince yourself not to think about her, the more you will feel tempted to, because the forbidden fruit is always the sweetest. Instead, relish those moments when you're alone, and reflect on what a great day you had, and play them over once again in your mind, as though you're letting her experience your happiness.
You must do the thing you think you cannot do. Don't look at a day as being something you have to "get through", think of it as something you need to seize and live with passion. Free those painful emotions, let them flutter away. Once you let go, and dream in technicolor, peace will be on its way.
Think of it this way: Your girlfriend would want nothing more of you than your happiness.
"To live remains an art which everyone must learn, and which no one can teach." ~ Havelock Ellis
"There are no monuments dedicated to me and my name will soon be forgotten, but I've loved another with all my heart and soul, and to me, this has always been enough." ~ Nicolas Sparks
I can tell from the way you are unafraid to express yourself that you will lead a meaningful and purposeful life, so let go of your inhibitions and live them for her.
Edit: Having read Lark's answer, I'm a little weepy with nostalgia. Nolan, I really hope things will work for you. Remember to always have faith and believe in a silver lining, because you will see the sun again soon.