What is the best way to deal with the feelings of jealousy, suspicion and regret that trouble me after I saw my wife's messages from the period before our marriage, which were for the purpose of getting to know someone for marriage?

The questioner's regret for spying on his wife's account is a good thing, and it is a forbidden act from which one must repent. He must stop searching into her past and not allow doubts to settle in his heart. He should repel these bad feelings from himself, for Satan strives to cause separation between spouses. He ought to treat his wife well, and jealousy without suspicion is blameworthy.