Your safety is the priority here, and knowing where he is gives you information that actually helps you stay ahead of the situation rather than being caught off guard.
The starting point is VINELink at vinelink.com. VINE, which stands for Victim Information and Notification Everyday, was built specifically for situations like yours. It is a free public tool that lets you search for an inmate's current custody status by name, and more importantly, it allows you to register for automatic notifications. If his status changes, if he is transferred, released, or escapes, you get alerted directly. That notification feature is the most valuable part of the service for someone in your position.
To search effectively, you will need to know the general area where he was arrested three years ago, specifically the state and ideally the county. From there you can search the state department of corrections database if he was sentenced to state prison, the county jail's inmate locator if he is still in county custody, or the federal Bureau of Prisons locator at bop.gov if federal charges were involved.
If you do not know which jurisdiction handled the arrest, start with VINELink using his full legal name and work through the states you believe are most likely. InmateAid's inmate locator is another resource worth trying if VINELink does not surface results.
Once you have confirmed where he is, registering for release notifications through VINE is the single most important step you can take. You should not be in a position where you find out he is out after the fact.