If you can only afford diamonds that were smuggled out of a warzone and used to fund the deaths of other humans then you can't afford a diamond.

Buy second hand.

Buy other types of stone.

Covet lifeless stones a little less and living people a little more.

You're the beholder, it's your eye you're pleasing - don't assume diamonds are the most beautiful stone or some sort of physical equivalent to love just because everyone told you so. It's just a hunk of rock.