Mistrustful

I'm not mistrustful; I'm simply cautious.

Source: tatoeba (10250318)

Tom is becoming more mistrustful.

Source: tatoeba (10794686)

Indeed, the little flame seemed conscious of its own inability, and burned with a wavering and mistrustful flicker, as if it was discouraged in view of the task set before it, and had more than half concluded to go out altogether.

Source: tatoeba (11641286)

[…] I hold it cowardice To rest mistrustful where a noble heart Hath pawn’d an open hand in sign of love;

Source: wiktionary