Just to add another space related answer:
An eternity has passed
For a star to become a black hole it has to pass several million years.
I killed my true love and my neighbors, but they have not left me
This is a story about a solar system and his star. The star become a black hole, and in the process killed his true love, an earth like planet, and the neighbours, the other planets.
I had the power to raise the seas, and most things you knew and loved
Everything we see here on earth is thanks to the sun. Everything.
Edit by @Tosen: Correction: this explanation does work, however, an expanding star is hot enough to evaporate (raise) just about everything.
I had the power to destroy you all, but you still managed to step on me
Sun flares can kill us all. And the earth like civilization could somehow step on his star. At night obviously, too hot! No seriously, no clue.
Edit by @Tosen: Correction: Expanding stars destroy everything. Hollywood stars on sidewalks are stepped on.
You forgot about me even in your homes, while I stuck around
We don't see the sun quite often while we are indoor. Also with artificial light we don't need it, but still it is outside.
Edit by @Tosen: Correction: This is a good explanation. But I was thinking gold "star stickers" that kids are given for good grades.
Your weapons… You lowly, violent humans and your guns --
Their fundamentals managed to kill me
While trying to harvest solar power the civilization managed to start some kind of destructive process for the star.
Edit by @Tosen: Correction: Ultimately, the depletion of "fusionable" elements (iron!) is what kills a star.
But even in the darkness of death, I am still very much alive
The black hole still is pumping matter, no signs of ever stop...