Loneliness.As per my thinking its nothing but as you like to do everything you like to have anyone you like to go anywhere and during this journey anyone can't join may be there's something they don't like and that's  why they leave you and you got alone.

So its not your choice but its by someone's choice.May be they loose a lot of things and you got a lot of things.Try to be patient cuz Loneliness isn't that bad.