Re: Marriage to a ghost prevents a new one even after he disappears forever

Your best bet on getting this fixed would probably be installing the MCCC mod and clearing all relationships. I'd suggest saving your game right before doing so, so you can go back if needed. If you really want to be safe, make a back up: https://sims4.crinrict.com/en/2014/09/backups/
What JP is saying is correct, that is the bug report that belongs with what you're experiencing, only the workaround wouldn't work for you.