Why are you jealous of your partner's dead wife?
You probably wonder if he can ever love you as much as he loved her; after all, he never chose to leave his dead wife, she just died, which was beyond his control. And you may never know that answer to that question. But be happy for what you have, don't drive yourself crazy about things you can't change anyway. He is with you now, so accept that and make the most of it.