It seems pretty clear that it's about a break up. He clearly loved her, and he is finding this break up extremely difficult.
"But instead we wage a war that can't be won" - This suggests they tried to fix their relationship, but it was already gone.
"But my attempts of piecing life together leaves me alone" - This suggests that after trying to fix the relationship, it just made him feel a whole lot worse.
"I stand on the ash of all I've ever loved" - This is him over thinking about the past, i.e. their relationship.
It seems pretty clear that it's about a break up. He clearly loved her, and he is finding this break up extremely difficult. "But instead we wage a war that can't be won" - This suggests they tried to fix their relationship, but it was already gone. "But my attempts of piecing life together leaves me alone" - This suggests that after trying to fix the relationship, it just made him feel a whole lot worse. "I stand on the ash of all I've ever loved" - This is him over thinking about the past, i.e. their relationship.