Why the amount of BNB in my binance wallet changes without me buying or selling that? Actually first I bought 1BNB some time ago, now it's just 0.05 in my wallet and during the time I was seeing it changes weiredly!
You enabled BNB fees. So for your trading, Binance uses BNB instead of base/quote currency. You can read more about it here https://www.binance.com/en/support/faq/115000583311-Using-BNB-to-Pay-for-Fees