Why do people leave?

I was talkin about this topic to a frnd . I asked him *how can we let them go?*
He simply replied *this is what we do ..we do care about the people knowing that they'll leave .but still we do care about 'em . But when they leave . We let 'em leave. moving on is in our dictionary*
He also said *moving on is our last option*
But then i asked *why do they leave ? why ? Why dont we leave*
he replied *leavin us is their last option but movin on is our*
For a moment i blacked out as they were lots of question popping in my mind .i lost myself in the air of rumination , thoughts and confusion.