Is dexamethasone a positive or negative ion?

Positive ions are called - Cations Negative ions are called - Anions

Since it is a metal it forms positive ions.

Because that is how the universe was made. The law of charges states that opposite charges attract.

To become more stable: positive+negative=neutral. Neutral is more stable than positive and/or negative.

Negative ions have an excess of electrons while positive ions have a deficiency of electrons.