I really want relationship advice but I am scared to speak to a friend or family in detail about it incase they judge my partner.

Me and my boyfriend are both in our 20s, he smokes a lot of weed. (I knew this when I met him) – but not to this extent.
We’ve been seeing each other since July last year .
We are about a 2/3 hour train journey away. So the distance can be hard for both of us at times.
Recently I’ve learnt that he has severe depression. I’m finding it so hard to be in a relationship with him and I feel so guilty for saying that. He is so good to me and he makes me laugh, he’s thoughtful, all my family love him, he used to make such an effort with me, but recently I feel like things are going downhill and it’s completely out of my control.
He shuts himself in his room for days and doesn’t text me much anymore. (I assume because he is sleeping) We used to call all the time and now I feel like he doesn’t want to talk to me. When I tell him this he just denies it and always has a reason.
I feel lonely a lot of the time, he has opened up to me and cried with me and I’ve advised him to see a doctor or therapist but he won’t have it. He doesn’t listen to anyone. He blames people around him like his family, and even when I try and find solutions he will still say his life is shit.
I try so hard to make him happy and try and let him know I care about him. I travel to see him often despite working a lot. the other day I saw a notebook in his room and I know i shouldn’t have but I read it, and it was pages long about how much he feels worthless and can’t make anyone happy.
This makes me feel so anxious as his family has a past of suicide from when he was young.
I’ve tried to be mature and communicate with him about our relationship problems but he instantly gets defensive and usually snaps at me which causes me to bite my tongue and I feel like I’m bottling it all up. I usually end up crying out of frustration that I can’t speak to him or say what I need to without him saying things like “obviously I’m a shit boyfriend” and “I just can’t give you what you need”. I’ve spoken about breaking up, he will twist what I’m saying (or just not understand?) and I usually feel so guilty for telling him how I feel.
I feel like I’d be leaving him at his lowest if I left him now. I wanted to stick with him and we can look back on it and say it was a rough patch. I’ve spoken to his mum, she has said things like this has happened before, all he wants to do is smoke weed & he doesn’t help himself.

Last night we were fine but I felt so distant from him, he smoked a joint before bed, and then he had his back turned to me and I started crying just bc of how lonely I felt when he was right there. He got annoyed that I was crying he asked what was wrong but I just said I didn’t know because I was scared to start an argument and he got so snappy saying he just wanted to sleep. I felt so awful and thought in my head that’s it, I can’t do this anymore. In the morning he turned and cuddled me and said please don’t leave me. And I said I won’t.

I honestly don’t know what to do anymore. The thing is, everyone that knows him says he’s such a good guy and he is. I just don’t know if i can put myself through this forever.

Before I met him I was so confident and independent now I feel so weak, I can’t make decisions. I feel like I have lost myself being with him but i really do love him.
I just want advise what would everyone else do in my position? I really wish things were the same as they used to be, I just don’t know if it’s healthy to be with someone who makes me feel this way when things are bad.