I may not be there to see it. I hope I am, and maybe then we could have this conversation in person. However, things do not always work out the way we hope.
I have faith in you, Harry. I know that you will fight this evil that threatens our world and I have faith that you will win. I hope you will accept some advice from an old man who has seen and experienced much.
I know you have lived for the last six years with the pressure of being the Boy Who Lived, the saviour of our world. This will prepare you in some way for what will come. People will laud you, will want to celebrate you as the greatest wizard of your generation. They will want to know you and will want to use you. You will be fêted and frowned on, praised and criticized. It is easy in these circumstances to go to one of two extremes. To lord it over others, to expect the adoration of millions, to become the worst version of yourself. Or, you could try to live up to everyone's expectations, to feel responsible for everything and serve everyone.
Either way you will lose sight of yourself, and what is really important. If you feel that you cannot care too much for the individual, because it will make them a target, a means to hurt you, or because being tied to an individual will mean that you cannot do what you need to do for the whole, then you will have lost your greatest strength. It has been said, and truly so, that those who have nothing to live for, have no reason to fight. Allow yourself to love and to be loved. Do not push those away who would be your strength in the darkest times.
What your enemies will see as your greatest weakness, to put the life of another above your own, is in fact your greatest strength. No matter what power you hold within yourself, you are exponentially stronger with the support of those who truly love you.
Now you may well ask, what does an old man know, what right do I have to tell you these things. I have a little experience of the kind of fame, and the pressure that goes with it, that will follow. I have also fought, and led in the kind of war you are facing. I could so easily have found myself going down a dangerous route, concentrating on the whole, on the greater good, not letting myself get too close to any individual because I might lose them or be forced to sacrifice them. Fortunately for me, I met my very own immovable object and irresistible force rolled into one. She forced me to realize that all the sacrifice in the world meant nothing without love, that no matter the fact that my cause was better, without it people were just pawns and I would be no better than the other side.
If you are reading this, it means that I am no longer with you and cannot explain in person. I have asked another to help you understand what I have written, after all it is as much her story as mine. I would ask you only one favour, Harry. Be gentle with her, she will be dealing with a great grief, however much she hides it, and some of these memories will be painful for her. Do what you can for her. Ask for her support, and give her yours, for she loves you as much as any mother would.