Definition:
This fallacy simply paints an issue as one between two extremes with no possible room for middle ground or nuance or compromise

Either/Or or Black/White, False Dilemma, or Excluded Middle Fallacy

Example:
Fallacy Ex: “You either support George Bush or you support the terrorists.”
“You either for me or your against me.”
Fallacy Ex: “She loves me; she loves me not.”