There a lot more to magick than just ceremonial aka “high magick”, there’s also intuitive magick, and “low magick” which tends to be more tool free might use herbs and crystals, sympathetic magick, and is more common in witchcraft and pagan oriented communities than magickian ones.
Have a look at this and see if it resonates:
I would also recommend this tool free ward tutorial:
Did you enchant it to do something? Black crystals generally absorb negative vibes, but based on your intro it sounds like you have a bit more than that going on and would need to up the ante.
The above techniques are ones you can do stealthily in company while sitting looking like you’re watching TV or reading a book, or in your room, or in the shower, leaving no trace for suspicion.
I’d say as stealth is a priority, just a simple bracelet of jet, obsidian or onyx will all work and can be inconspicuous under a sleeve. Enchant it simply placing your hand over it and using your will to kind of program it to protect you against unwanted energy coming in. If you’re still a pagan make it into a talisman for your god and ask it to protect you.