The addresses you see in your wallet are changing because every time you send or receive cryptocurrency, your application will change to another address. But you must keep in mind that your previous address is still yours, it is still valid, it has not been deleted and it will not expire, it is considered a derived address.
A wallet can manage thousands of derived addresses and all of them are yours. These addresses do not expire and the value in cryptocurrencies that you see in your wallet is the total balance, i.e. the total of all the entries and exits between all your addresses.