Oh Sweetheart, I understand and I'm sorry about the loss of your friend.
If you love him and want him to really miss you, too, then realize he is in London to study. He won't be able to have daily conversations with you like before. You have to get really busy here so that when he does communicate, you have cool things to talk about.
He's in an exciting new environment and he will be trying to find his way around there and make friends while he is there. You will have to understand this. You have told him how you felt. As hard as it is, you should try to just get very very busy. He knows. Let him think on it.
I know it hurts, especially when you are used to talking to someone all the time. You've lost your terminal! ( the person you exchange ideas with all the time) You need to try to find new friends where you are and spend time with other friends you already have to take up the slack of him being gone. Otherwise, you will bombard him with communication and that you are upset and depressed. There isn't anything he can do to help you because he has to be where he is to further his life. Don't upset him.
Get busy so when he comes back you have a million things to share with him, like he will have with you. Besides, if you stop mailing him-he might just really miss you and it may prompt him to keep in touch more once he settles in.
I know it's difficult, but you also have to think of yourself and your own future. Don't be discouraged, but what if he doesn't feel the same? The thing is-not to waste time. Don't wait. In the back of your mind, you can know how you feel and be hoping he comes back and missed you terribly, but in the meantime-have a plan B. Men do, trust me. They go so far as to set up plan b before they have even left plan A! So, just focus on you right now. Work out, take classes, meet new people. Get out of the house or you will go crazy. Try to get your attention off of him.
If you know any Scientologists in your area, you could ask them for a "Loss of a person" assist. It is a very cool thing you can get that helps a person handle it when another person dies or leaves. It is very effective, so if you know anyone or if there's a church near you, you could find someone to give you that assist. It's free. You just have to find someone to give it to you who knows how.
Good Luck, and chin up. It's going to be ok in the end.