Cancer Man is a Water Sign, having Moon as its Ruling Planet. So, you have been with a Cancer Sign, and you are about to deal with him in any matter in Life, like Work, Study or in a relationship, and you want Answers about him.
So, in brief, Yes, a Cancer man can be Trusted in different aspects of life, especially in a relationship with him. He can keep your Privacy and never breach your Private thoughts with others. He can be trusted with money related Authorities, but do your Security and Paperwork First before giving any Authority to him, for your Safety Purpose.
If you want to secure a relationship with him, and you feel that he has some Past life related to his Ex-Girlfriend or ‘S, then you should make him clear about Marriage with him.
Cancer Guys never Forget his Past, whether it is Good or Bad. So, if you want him to make a Trusted Person, then you must have to become best than his Ex, and the best way of making you better than his Ex is by offering him do Marriage with you.
By taking this step, he will eventually be started forgetting his Past and get closer to you, and become more trustful in Relationship.
Where it has been seen that a Cancer Man tells a lie to save someone’s Respect, Dignity or for making someone’s relation better if getting worse.
He prefers to keep Quite rather than telling lies.
Where there is the direct involvement of Society where he has been brought from Infant to a Man. He has a kind heart, but if he is raised in a Lier, Low level, and Wicked Family, then the Probability of deceiving in him is quite high.
So, you must take an eye on his Family Background too, otherwise, he is a Trusted person at all because of his Traits.
Best of Luck!
Reference: I have taken some Help from this Site: https://www.astrology-zodiac-signs.com/man/cancer/