How to regain trust after it's been broken?

My husband's ex girlfriend was trying to break us apart for few years after our marriage. He is a passive guy and I ended up giving him ultimatum to fully cut contract or I'm leaving.

He did block her and deleted her number but she is still trying to reach out which is showing as notifications. He never did anything to violate my trust but my heart is not in peace yet.

Will I really be able to trust him with time or time never really heals anything?
How to regain trust after it's been broken?
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