If someone's husband or wife has died, they are a widow (female)/widower (male), and the dead person is called their late husband/wife.
A child whose parents are both dead is an orphan. They might be adopted or fostered by someone.
If a couple separate, they stop living together, sometimes as part of a legal arrangement. If this is a trial separation they may get back together again. If they divorce, they end their marriage through a legal process.
The person who they were married to is their ex-husband/wife or their ex (informal).