CGT on spending or paying bills

while ive learned tons about our dreaded cgt over the past few years, there’s one part of it i still want to get straight in my head …

as i understand it, if you buy crypto, for example, and keep it untouched for a period of time, then sell it for profit, in aud terms, the gain is included in your annual income and thus taxable

but – what i dont fully get is that if i buy, for instance, 1 btc (could be anything, even usd or some other fiat), when it was worth, for arguments sake, 10 aud, and then keep it for a while, but decide at some stage to either spend it (on goods) or pay a bill with it (pay for services) how this may make me liable for a capital gain …

so, i buy 1 btc at 10 aud, and then later on it’s worth 100 aud, so a capital gain of 90 has been made, on paper, but NOT YET REALISED, then i pay a 100 aud bill with the 1 btc, ok so ive paid a bill, and used up my 1 btc, but – do i still owe the ato money for a gain? in other words, im having trouble understanding the difference between making a capital gain, and receiving the windfall in cash after the disposal, and spending the windfall on a good or a bill, to me – that is not really a capital gain, its just spending your money, even though youve had the good fortune of your purchasing power/bill pool having increased over time