When you make a connection with someone, that connection always remains in the recesses of our mind. Though we might not pay attention to that connection, we are secure in the knowledge that we can go back to it, if we wanted to. But once you realize, that there is no going back, that the connection exists but the person at the other end of the connection is no more, it makes you feel really helpless and I believe helplessness is one feeling that can one can quite never make peace with. It is that helplessness that I believe that makes you want to cry. When a person is helpless and can do nothing much about a situation, the only relief they seek is in tears.
And yes, its a lifetime thing. No getting away from it. Death unfortunately is that final!