Welcome to the forums and thank you for reaching out.
It must be heartbreaking to see your partner suffering as he is. I'm glad he's seeking treatment and that he has your support.
The best you can do for him is to stay by his side regardless of what he may say. It's normal for people with mental health concerns to feel like they are a burden on their loved ones, but it's the support of these very people that can help them get better. Reassure him that you choose to be by his side, even if it may get tiring for you to repeatedly do that. He is not rejecting your help, but in his own way, he's trying to protect you from his problems.
Please remember to take time for yourself as well and safeguard your own mental wellbeing. Being a carer isn't easy and your partner's bad days can leave you feeling emotionally drained.
I hope you will be able to connect with other carers in our forums and find some support in their stories as well.