From the way I understand how this works, each trade of ETH creates a reportable gain or loss transaction

1) when you sold ETH and purchased the NFT,  the price of ETH on that day, compared to when you first purchased ETH is a reportable gain or loss transaction

2) then when you sold the NFT, and purchased ETH, the NFT is a reportable gain or loss transactiion

3) when yiu eventually sell .5 ETH, there will be a reportable gain or loss transaction.  The cost basis is the purchase price in 2) above.