It is about losing an important person. He suddenly disappears from someone's life, through the fault of a third person. Not being able to see this unique person anymore, not being able to touch him, not being able to hear his breath next to you and noticing that his smell is slowly and steadily leaving the room can drown you. 
Life goes on, though. How do you turn grief, pain and anger into something positive? 
How do you process it,
to look at pictures without feeling that pressure in the upper body and to sing and listen to songs without crying from sadness? It seems impossible...
Trying to deal with the pain and to hold on to memories despite loneliness and to gain strength from them is probably the only thing left.