Jealous means "apprehensive or vengeful out of fear of being replaced by someone else." It can also mean "watchful," "anxiously suspicious," "zealous," or "expecting complete devotion." The last is normally applied to God.
The noun form is jealousy; the adverb form, jealously.
Envy means "to bear a grudge toward someone due to coveting what that person has or enjoys." In a milder sense, it means "the longing for something someone else has without any ill will intended toward that person." Envy can be a noun or verb.
The adjective form is envious; the adverb form, enviously.
Suspicious means "being doubtful or mistrusting" or "being convinced of someone's guilt based on insubstantial evidence." The verb is suspect. Suspect is also the noun referring to a person suspected. The noun form is suspicion, and the adverb form is suspiciously.
A person envies someone towards whom he has ill will because of that person's success, achievements, and the like. He envies something that belongs to someone else and to which he has no right or claim. He is jealous of intrusion onto something that belongs to him or upon which he maintains a claim.
An envious attitude is always negative. A jealous outlook is usually negative but it can be positive, depending on its object and inclination. For example, a man may be jealous when another man talks to his wife (negative); however, a free people must jealously guard their liberties if they want to keep them (positive).
A person can be suspicious of someone else from unfavorable signs or from a knowledge of past wrong, even without reason.