He is very suspicious and doesn't trust people easily.
猜疑心から、友人の言葉を素直に受け取れなかった。
Out of suspicion, I couldn't take my friend's words at face value.
猜疑心 refers to a deep-seated, persistent distrust of others, while 疑心 is a more general term for a feeling of doubt or suspicion.
猜疑 (suspicion) + 心 (heart/mind). 猜疑 is a compound of 猜 (envy, jealousy) and 疑 (doubt).