I would recommend you to use apps like blockfolio. They keep track of your investments and calculate things like loss and profit for you
Not only for 1 BTC, if the buddy bought same amount of BTC let say "X" in each transaction.
X can be 1 , 2, .5 or any positive Real Number.
PS: Pooya87 explained it so nicely, I do not think you need any further response on this topic, so lock it. Using the app is ok but knowledge of basic mathematics will not hurt you