How can we get our relationship back after a mental health crisis?

I have been with my boyfriend 3 years. 6 months ago he had a mental break down due to a traumatic event in his family. I have supported him to seek mental health. Supported him financially tried to remain patient while he withdrew but I am at the point I am at the point I feel taken for granted and so alone even whilst in a relationship. We never have sex anymore even though that as a big part of our relationship at the beginning. Most recently he completely forgot our anniversary. I don't want to leave but I am not sure how much longer I can keep staying and waiting for him to get better when I feel he puts nothing into our relationship. I know most of it is because of his depression and ptsd. I just feel completely drained putting so much in and getting nothing back..

How can we get our relationship back after a mental health crisis?
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