There's an app made by nokia (see link below) called nokia custom dictionary. It lets you see all your words and to delete them as you please. It's good.
That said, it's worth knowing that if you repeatedly select the second or third option in any predictive text word, the system will learn after a dozen or so goes. No need to delete the ex-partner's name just cos it's similar to the new one; just stick with it and the phone'll soon figure things out!