Depression

Good evening Ladies

My boyfriend have a history of depression and whenever he sinks into his depression he goes into isolation and I just feel so helpless because I want to support him so much but I don’t know what to say or do. On one hand he wants to be left alone to deal with it but in my heart and from what I have learned about depression I don’t think I should just let him deal with it alone. I do want to respect his wish but again I know it is the wrong thing to let him isolate himself. what should I do? Please help