Man...Reading this is heartbreaking..to say the least. I'm so so so sorry about your loss..
However, I'm SO proud of you for how far you've come. You've come a long way, and you know, some people would have just given up if they felt like you do. You have made it thus far, and you've done it in such a great manner. You're a very strong guy, and I believe in you. You're very fortunate to have a family, and a girlfriend that loves you as much as they do. Don't really forget about what happened, more accept it. Accept that he's gone, but think about it in a positive way, he had cancer, and that is a disgusting disease, but now, now he's in a place where he no longer is hurting, he no longer is suffering. But, he's not completely gone, like someone mentioned above, he's in your heart. He always will be, he's always going to be watching down on you, and most of all, he will always be PROUD of you, for living his life for him. Do that for him, live his life for him, do things that make you happy, and make yourself happy for him.
I have much respect for you, brother. Again, I'm so sorry for your loss. Please keep us updated on how you're doing, and you can ALWAYS come to me or anyone else in the community, because we all love you, and we are all here for you whenever you need us.