Everything in life is impermanent. Even your own body starts dying from the moment you are born. All relationships end. Sounds cold and terribly depressing, I know, but the good news is that bad feelings are impermanent too.
When something absolutely wonderful happens to you and you feel the best you have ever felt in your life, that feeling will eventually fade away -- EVEN if NOTHING changes. The opposite is also true. As bad as you feel now, the feeling will eventually subside. So even though it's disappointing that no good thing will last forever, it's comforting to know that no bad thing will last forever, either.
We say that in time everything accumulated will be scattered, everything built up will fall, everything born will die, everything joined will part. But if you really, REALLY think about it, with your heart, it's not pessimistic. It teaches you to enjoy what you have in each moment, without reservations or limitations, not to fret over the future but to treasure the moment you are in, because you can never get it back and you don't know how long it will last.
Ask for one hour when the two of you can just be together in the present. Don't talk about the past, don't worry about the future, don't hold each other to ANY expectations just for that short time. Don't have an agenda like prolonging the relationship, ending the relationship, or one person getting their way. Just one perfect hour to celebrate each other, no grudges or plans. It's entirely possible to worry about the future so much that you totally miss out on the present, or to cling to something so tightly that you choke the life out of it.
You seem to be a beautiful, caring, and thoughtful person, and I hope you would select the same type of person for yourself. You have suffered a lot of terrible losses, and I hope that you are not expecting your girlfriend to be able to fix all that heartache. A relationship is just the feelings and interactions between two people, it really does not have the ability to change feelings and events outside of itself. Another person can not MAKE you happy or unhappy - that comes from within yourself. Making someone else responsible for your feelings puts an unfair burden on them, and it puts you in a very precarious position as well. I wish you all the best.