Am I sinful if I refuse to have intercourse with my wife, or if I tell her not to ask me for intercourse in cases of illness, exhaustion, psychological instability, or anger towards her?

There is no sin upon you if you abstain from marital intimacy with your wife in the aforementioned circumstances, as long as it does not reach the point of harming her. The husband must engage in intimacy with his wife according to her need and his ability. Good companionship between spouses necessitates that each considers the other's state, and avoids harming them through excess or neglect.