Normally, I don't struggle with grammar, but this has me stuck. In this sentence, "One could call him an addict, because women were his drug," would you leave drug plural or singular, or is there something else to do to fix that?

Leave "drug" as singular. Sometimes we say, "women were his drug of choice."

In the sentence, "One could call him an addict, because women were his drug," the word "drug" should be singular. However, it is important to note that correcting grammar is subjective and can depend on the context and intended meaning.

To determine whether "drug" should be singular or plural, you can consider the following points:

1. Noun Agreement: In this sentence, "drug" is intended to represent a singular concept, being women as the addictive substance. Therefore, it should agree in number with the subject, "women," which is plural. To maintain concordance, "drug" should also be plural to reflect the plural subject.

2. Figurative Language: The sentence uses a metaphor, equating women to a drug. In such cases, it is common to use the singular form of the noun representing the substance or concept. Therefore, the word "drug" should be singular.

Considering these points, the correct form of the sentence could be: "One could call him an addict because women was his drug."

However, it's worth mentioning that this sentence might still sound a bit awkward due to the discrepancy between the plural subject and singular verb. To improve clarity and readability, you may consider rephrasing the sentence to avoid potential confusion.