Endlessly / ceaselessly (…不已)

…不已 (… bù yǐ) is a formal complement attached after a two-syllable verb or adjective, almost always one with emotional weight, to say the state "does not cease": 激动不已 = "deeply stirred, unable to calm down"; 赞叹不已 = "endlessly full of admiration". Here 已 means "to stop, to cease", so 不已 = "won't stop". It belongs to written or literary register; in speech one would say 激动得不得了 or 一直赞叹. It only fits two-syllable, intense bases (后悔不已, 感慨不已, 痛苦不已), never a concrete action verb like 吃 or 走.