I can resinate with you on this as I was recently in your position, actually more so an ongoing 2 year push/pull or otherwise known as the carrot chasing the stick. I am not sure exactly the full brunt of your situation, however, if you have already tried to communicate your support/desires/needs and he still is not doing anything about his [depression], then I would best understand that this is more about him then it is about you.
I want to let you know that this is a common situation in unhealthy people. I do not believe in unhealthy relationships. It's an unhealthy person that unbalances the dynamics of a relationship. Let's peal back the complex stuff.
When there is what I like to call an unbalanced relationship (use an analogy if you'd like), it is mostly caused by one person who is having difficulties with accepting themselves as a person or in simple terms, do not value themselves.
Now, the golden rule is, if one does not value themselves, then they do not value others, if because of this, they cannot commit to themselves so therefore they cannot commit to others. They both tie in with each other.
I want you to know that you have the courage to make the best and most appropriate and healthiest decision for yourself and only you can do that. If you cut this person off, don't beat yourself over it because you have shown that you are a compassionate and beautiful person and for also reaching out for advise. That is something that a healthy person values - support from others.
Keep your chin up and smile.