You ran the first 100 too hard
The fastest 200m runners do not sprint the curve flat out. They run it fast but controlled, then unload on the straight. If you attack the first 100 like a 100m race, you build a lactate debt you cannot pay back, and the fade is the bill. A well-run 200 is usually about 1.0 to 1.3 seconds slower on the second 100 than the first. Much wider than that and you went out too hard.

