First and foremost, depression does make you say and do horrible things even to the ones you love. Depression is also different for every person so saying my depression never made me say xyz holds no weight. None of us are your partner and none of us are going through what he is specifically in terms of his depression. However, someone going through their own form of depression should, I would hope, be more able to understand that.
First, he technically kept a personal diary and his partner reading that is a violation in the same way a partner snooping through texts would be.
Depression is nasty and writing is, for many, a legit way to cope when it gets too thick. That does not mean what is written is whom that person is truly or how that person feels truly.
For him, writing is clearly his initial stage of coping. To have that violated would certainly make anyone defensive if not hurt. While what he wrote was upsetting, it should have been a space that was respected.
Now this doesn’t mean OP can’t feel hurt. Of course she can be hurt. As I stated before, having a partner or family member with depression hurts and it’s hard to not take it personally.
So, OP, shouldn’t be discussing this with a board of people that can not properly explain the way depression works and the way it can present itself. She should be making an appt with a therapist to discuss it with them and to discuss her own feelings that she is struggling with and will struggle with at times in sticking by a partner with depression.
It’s perfectly fine to say it’s too much and not a healthy dynamic for her if that’s her decision. However, it’s not cool to have feelings like he wanted to be vindictive or that his illness is just an excuse.
The reason he is turning around and snapping is because he had a trusted and stable place he thought he could unload all the “dark stuff” of his depression in times of deeper depression and now that is being thrust back to him and filling him more than likely with a lot of feelings of guilt/reprimand. Anyone would fill a range of emotions even resentful for having an illness being held against them especially one they’re trying to battle. More than likely his depression is coming full scale because now he is feeling backed into a corner for potentially things he doesn’t feel he truly feels when he is having a “good” day. He certainly feels sorry for having depression and having it cause him to be like that but it’s also something he cannot help or control. Depending on how OP approaches it, which is why the help of a therapist is needed, it can feel like he’s being attacked for his depression.
Depression makes you sexually not attracted. Depression makes you feel like your relationship may be too hard or too difficult and maybe it’d be better to be alone. Depression makes your mind turn to places you never want to go to. People don’t say battling depression lightly and those battling depression certainly do not love the people closest to them less. It’s an illness.
So, by all means, let’s advise the OP not to be with him till he gets to a better state, not to be with him if it’s taking a toll on her, to get him help, to get herself help, or so forth…but let’s not make light of what depression is and what depression does.