Death spells is a bit of a grey area. Some see it impossible to kill someone with a spell because you're playing god. On the other hand, it is seen as an intense curse, focusing more hatred and negative energy upon the person.
If you are convinced then try, but I would try to forgive and forget [and cut them from your life] but I know not everyone can do that, so if you have spent a year reflecting, trying to forgive, but this is the only option you feel will work after exhausting all others, then go for it, but if anything happens [backfired or works] you wished for it, so live with the consequences. [Guilt of taking a life, even an enemy, but it could backfire and effect a loved one]