Doveryáy, no proveryáy.
For this situation, you might translate that as "trust, but test" rather than "trust, but verify".
It would be devastating to find out that your partner has been cheating and that you are both HIV positive or have gonorrhea or another sexually transmitted disease. Many relationships that are monogamous don't stay that way forever. Many times it happens without both partners being aware that the relationship is no longer monogamous.