How do you define loneliness?

Have you ever wondered what loneliness actually means. What are we comparing it to? Is it opposite of happiness or is not not being surrounded by people. Who are these people whose absence makes us lonely? Or is it this one person who has caused the void in your heart? Is it because we miss this person or just got used to them being someone?

Loneliness for me more than being alone (literally). My soul is empty and void of joy. It seems the one I loved not only took my heart with him, he took my ability to feel at peace and content with him. I surround myself with people day in and day out and yet I stand alone looking at their smiling faces. Why don't I feel the joy in life like they do? I have always fought battles and have always come out alive, then why am I already dead in this battle before I have actually fallen to the ground?

Cancer, My Love, Parents, Siblings, Friends - Can I have any more battles to fight at the same time? I thought I had so many to love and who loved me and then why do I stand here alone fighting all these battles today? Why am I lonely? Why is my heart sinking with every step I take? Why do I go ten steps backwards with each step I take forward?

Too many unanswered questions. Too many battles for one person to fight at one time. I struggle to find the reasons to go on.