Hi,
It's always difficult to know how and what to do when dealing with anyone suffering with depression as they have a tendency to view things from a "skewed" perspective. Although your intentions are great they are probably being perceived as being a little overzealous. It's really important to people who are suffering from depression to not feel like they are a burden to anyone, and to maintain "control" over their life. I also think it's important to not let his illness become the focal point of your actions and behaviour. If you want to introduce healthier habits or lifestyle changes that you believe would be to his benefit, make sure that you involve him in the decision making process and aim for a win/win situation. People with depression tend to do better with predictability and the comfort of what they know rather than having to adapt to change. Implementing too many changes could be overwhelming even though their intentions are great.
You are coming from a good place and I'm sure that your partner knows this. Communicating your support to him is valuable. Offer him a good ear and the comfort of knowing that he can speak with you about how he feels etc. Being a good carer is all about support in any form that fits. Let him know that you're available in that regard. As with diet/exercise ask him what he would be amenable to and offer gentle encouragement without pressure. Slow changes will work better than a sudden change, as does with anyone let alone someone who is suffering with depression.
I think that if you treat his depression as more "matter of fact" than to focus on it as an anomaly that needs urgent special treatment/consideration, it will be better for him and you. If you refer to it too much by way of lifestyle changes etc it actually places more emphasis on it if you get what I'm saying. For example: when you sit down to eat your healthy food after you've exercised, both of you are making his depression take centre stage because the only reason you've done this is because of his depression. Try and keep things as "normal" as possible and introduce changes slowly.
It takes a while to come to terms with mental illness (depression) and finding your feet is part of the process. It's great that he is seeing a psychologist and wonderful to know that you are so supportive.
The key is to work together as one to find that balance so that you both find a place that is mutually beneficial and satisfying.
All the best
Janna ❤️