On Leaving

I hate it when people I care about leave or move away from me.
They tell you things like "No, it's not you." or "I've got some issues to solve for myself." but you're not really sure if they're being a hundred percent honest with you when they say that they need to drift away or transfer and stuff.
I guess this is just bitterness, to be honest.
I'm not a very clingy person, so when I cling to someone, then that person is really special because that doesn't happen very often. And because I get so attached to said person, the leaving becomes a bit harder to cope up with, in comparison to the regular non-clinging friendship.
Every person leaves for different reasons. One leaves by taking up a different college major from me, another leaves by transferring schools, and another leaves by just not being what we were being. I tell myself "I'm happy for you! You're doing what you want to do.You're doing what makes you happy!" but that's not totally the case. I end up telling them "Don't go away. It's such a waste." or simply (and desperately) "Don't go."
I tell myself that what I'm feeling is genuine concern, that I don't want them to leave because I see the potential they have in staying the same place where I am, but that's not totally true. Maybe a part of me feels that way when I say those lines, but most of it is driven by selfishness. The reason why I don't want them to leave is because I don't want to be left alone. I don't want them to leave because I don't want to go back to square one and start making new relationships to replace the old ones that don't need to be replaced. I don't want to make an effort in catching up with each other because then I'll be clingy and I don't want to be clingy.
I just... don't.
And I hate this selfish feeling. I want to be someone who can understand and accept the leaving, to be happy for these important people who are making their own journeys in life. I can't explain how hard it is to want to let people go but also anchor them beside you.
Friendship is hard, man.