I despise my brother-in-law
That's awful. Why do you dislike him so much.
He likes to tell me he has a better life than me and it is hurtful.
Although it is wrong to despise people.  It is understandable to be hurt by his petty actions.
He secretly wants me to burn forever in hell.
He told you that or are you assuming? It sounds like the two of you need to sit down with a mediator and talk about your issues.