When you trust someone completely, nothing they do is suspicious. When you do not trust someone at all, everything they do is suspicious.
That's why it's so important to value trust right from the start and be honest about even the little things.
Once trust is lost or broken, so much drama is created because everything, even the little things, are brought into question.
If someone has broken your trust, know that you need a solid boundary in place if you've decided to keep them in your life and allow them to rebuild it. You can't turn into a detective and follow up on their every move, looking for any other untruth.
If you believe can trust them, do so but with a boundary.
If you really can't trust them anymore, it may be better to be over. Neither they nor you would want to live in the new dynamic of mistrust.