Bitcoin is a currency. But it's value doesn't always depend on the limited supply. There is a production cost of Bitcoin. Miners need to buy Expensive mining rigs and spend money on electricity so that Bitcoins can be mined. Demand definitely plays a rule in determining the value of Bitcoin. There are other smaller factors as well. You can consider halving as a major factor that decides the price of Bitcoin alongside the production cost.

Bitcoin is a great store of value but not really a great currency system to be honest. It's slow and expensive so consider it as a great investment rather than a currency system.