What should I do if my boss has become hostile toward me?

The answer varies depending on the boss, yourself, the amount of time of hostility, and the occupation. Never fight back, even if you are right. They may use that as an excuse to fire you, and you will not get unemployment. If they manipulate you, ignore them at all costs, and do not acknowledge their manipulation. Try to look at the problem from their perspective, and do the work to the best of your ability no matter what. If they're hostile to you over text or email, keep copies of these for documentation purposes in case you need to turn them over to Human Resources.