Depression is a very complex illness. It takes a lot of time and effort to pull yourself out of it sometimes. It could be that he needs that time to figure out what meds or what combination of treatments works best for him. However, while there are a lot of things and different treatments, this isn't something you can just fix yourself. The bottom line is that there's no amount of loving or caring about a person that would be able to just make their mental illness go away. And if you aren't a professional mental health expert, it's above your pay grade and not your responsibility. As his partner, however, you can be there for him. I don't think it always has to be a huge thing either. It could just be keeping him company, helping him maintain a clean living space, asking how he is, or making small goals together. If small things like that are all you can do, that's okay. It sounds like you already might be involved in trying to help him & be there for him in that way though.

The only other thing I can think of would be that it always helps when a loved one is struggling with something, is to do research on it. Especially with mental illness, there's a lack of knowledge and a lot of stigma. So being educated as much as you can about it can help in learning ways you might be able to support people you care about