Sacrificial protection

Is it kind of dark that only ONE witch in history since the creation of the killing curse, loved someone enough to make this work?

Towards the end of The Goblet of Fire, Voldemort regains his body and is now able get past Harry’s protection since he shares a bit of Harry’s blood. He proves this by touching Harry without any consequence. Then he sets out to duel with Harry. But, if Voldemort had gotten past the protection, why did they make such a big deal out of it wearing off at the end of The Deathly Hallows? Or, if he hadn’t actually managed to get past the protection, how was he able to touch Harry and why did he try to kill Harry? Or is this a plot hole?

Also, I’m new to Harry Potter, so I’m not an expert on the lore, so it may be that.