I can't stop being mean and it hurts

My boyfriend does this stupid thing where when he's going through a bad day he gets so incredibly negative that anything I say he finds a way it wouldn't help. Every time he gets like this it's an argument because I can't handle the way he talks. I want to help but when someone I'm so attached to is so goddamn pessimistic it makes me want to die. It feels like it just means I'm not good enough to make him happy, and that my advice is just shit. So I get defensive and pissed off and I don't mean to. I really don't want to, but stopping myself physically hurts. I have to send and delete messages and take multiple minutes to reply once so I don't sound rude because I don't want to hurt him. It just makes me so fucking mad and I need an outlet, and not having one makes me feel like my chest is exploding. I just don't know what to do. It feels like he's just sucking himself into his hole and he absolutely refuses to get help, and him not getting help feels like a personal attack on me. I want to yell at him and myself and cry and hide away in a corner. I hate this