so you're fine with killing him and not leaving him? if you've found someone else, why not a banishing spell on your husband and moving away with your new beau? legally you could look into a restraining order.
death spells are a grey area in magick, some claim it's too much power for mortals to have, others claim it's a very powerful curse. if it was possible however it would require a ton of energy and focus. on top of that, would you really want the death of a person on your conscience?