Loneliness is characterised not by the number of people you are in contact with but the quality and loyalty of those you share a bond with. In the ebb and flow of things it is easy to feel as if you have security in the bonds you made previously but when you look to call on that bond you can find time works to erode relationships and the bridge is one way. No one can be blamed for this, it is just distance of interests, growth in opposite directions and aging that fuels it.