I feel like I don't understand the question correctly, can someone help?
I don't see why 8 is false (can't win)
So
I take 3 first, 8-3 = 5
Friend takes 2, 5-2 = 3
I take 3, the end I win?

At the start, you have eight stones.You take 3 first, 8 - 3 = 5. If your friend was enough clever, he would take one. At that moment, there are four stones left. Unluckily, no matter how many stones you take this time, you are sure to lose undoubtly.