How can I help my husband see he needs to get back on his depression meds?

Depression meds? Many patients with mental illness have poor insight and judgement. They don't believe they r sick and they don't take their medication. Usually family support is important and may be able to convince u husband that taking his medication is important for both of u and whole family. Sometimes if u convince him to seek family therapy may work as well.
Show him/ get help. Show him with specific examples how his medication has helped him and how he behaves with and without the medicine. Also ask him why he stopped. The side effects may be too much but he may be embarrassed by them unless you ask him straight out. Also ask his prescriber or therapist if he gives you permission to do so to help you help him. The prescriber may not even know he stopped his medicine.