I don't have many friends. It seems we have a limited amout of what can be called energy to associate with people. So we can't have any more friends than the energy allows us to.
Besides, a change of the context in which we live results in the addition of the people with whom we associate. It follows from this that the increase of frineds will force you to lose some of your friends whom you have had.
The entrance into the graduate school of philosophy has changed the context of my life. I live in a different way, for different purposes, with different values than I previously did. This has led me to get acquanited with new people, new friends. So, I have lost contact with some of the older friends because of my limited energy.
It should be sad. But, in fact, I don't feel sad at all. To tell the truth, the contextual change of my life seems to prevent me from feeling that way. I don't even feel like meeting them. If they invited me to get together, I might do so. But surely I won't invite them. This feels really strange. I have changed completely before I knew.