Master: An individual’s master is the person who has the power of procuring for him or denying to him what he wants or doesn’t want. - Epictetus
Your master is whoever controls the things you want, or want to avoid. If you want to be free, don’t wish for anything, or try to avoid anything, that others control; otherwise you’re a slave.
We can also enslave ourselves to things, not just people. As long as we love, hate, dread these things. Those who control them become our masters.
Change your hierarchy of values to lower the importance of external things.