when is too far too far?

i hate saying good byes.
i hate saying good byes but i've been doing that my whole life. elementary school, secondary school, high school graduation, work, bla bla bla, i had so many fairwell parties in so many different occations. i hated them, and i still do.
there's this old saying in chinese that all parties have to come to an end. i like that saying but i hate it at the same time. why do parties have to come to an end?? i'm having fun at the party dude, keep it moving!

but oh well, i guess separation is inevitable, so i need to suck it up and face it, which i did in all these years. now the thing is, after the physical good bye, the connection or friendship or whatever relationship it was should be still there, and you keep in touch with the person, and you still talk to them either over the phone, email or chat. then little by little, the chemistry that you guys had start to fade away, and little by little, you realize that there's not much left to talk about, the amount of emails that u get can be counted with one hand and all you get are those useless junkmails from erotic sites; or while both of you are online, it seems that the person is just another 'online buddy', you don't bother to open the chat window anymore.
ok, maybe i shouldn't generalize this. the examples given above are from my personal experience, k? do not take it personally.

what is what make people (or in this case, ME), feel distant from each other? does distance really matter that much? what kind of conversation should you update each other to stay connected? how do you know when the relationship is not as it used to be?
and when the chemistry starts to fade away, is it due to the lack of imput from one side or both???
or put it from a different perspective, what is what make people stay connected with each other?