If you need the difference explained to you, give your wife/girlfriend/mother/daughter) a plain stone ring to celebrate a special/significant event/anniversary and you will be provided an extensive, detailed pinpoint difference, that you will never forget (nor she will EVER stop repeating).
A diamond may be a pretty stone, but a stone, nonetheless. It is all in the presentation. Cubic zirconia is a pretty stone, and few women can tell the difference from a natural diamond, even with a jeweler's loupe. Chicks dig shiny and glassy. If she isn't told the difference, i.e., the presentation, she won't know the difference.
A stone of titanium is every bit as valuable as a diamond stone, but it ain't as pretty. Titanium ain't shiny and glassy. But, a stone is a stone, whether carbon, metallic, or some other earthly substance.
But, I'll admit, I've never given my wife a stone of titanium or cubic zirconia. Nothing but a diamond stone for my better half. And she IS the better half, make no mistake. About the only score I've ever made in my life.