It was dedicated to his mother. And as a motherless daughter, I can relate to every word in this song.
My mom passed away in 30-3-2017 and I used to listen to One Last Goodbye on repeat, I still do ..
I believe his relationship with his mother was strong like mine, many people will think "it doesn't feel like its talking about motherly love" but take it from someone who lost her mother, it does talk about motherly love. I can feel every word and relate to it.
And about "strength" I'll tell you about my opinion, or share my part of the story.
My mother was a strong woman, mentally and physically.
She went through a lot of things during her life (mentally), and then she was diagnosed with cancer and she was fighting with all of her strength, the cancer was aggressive, she had Leukemia - ALL, but to me she was like my super hero and one of the things I loved about her was her strength, but when it was her time I knew she wanted to stay with us, but it was her time to go and I remember telling her in the ICU room (you know I love you more than anything in the word, but I dont want to be greedy, if you cant handle this anymore, if you are fighting just for us and its taking all the strength you have, if you are going to a better place where you'll be free of cancer and pain, I'm letting you go mom) .. and thats when it hit me every time when the song goes : your heart yearned to stay, but the strength I always loved in you finally gave away.
Ps. English is not my mother language, so excuse my grammars. ^_^