What Do I Do

I’ve been w my bf 3 years. He always goes through up and downs where he is sad. Recently he’s been feeling it more. We think it could be standard depression but he doesn’t want to go to a doctor. This is affecting out relationship now because when he gets like this he gets easily irritated and kinda takes it out on me. He works all the time and even tho he’s young (20) I think he should slow down to enjoy his life more especially because he’s very grumpy and tired after work. I’m extremely worried rn because last night he said that he’s bringing me down and that he wants me to be happy and he thinks he’s a bad bf (he’s very hard on himself all the time and overthinks) he said “u don’t do breaks” cause no I don’t see the point in a “break” to me u should just break up then. He mentioned a break only because he thinks I’m not happy and I cry if I said something hurtful when he’s in a “mood.” After we talked he said he’d talk to his mom abt the way he’s been feeling. What hurts is that he’d rather do a “break” which would help nothing instead of just going to see a therapist like he should. I love my bf so much and I don’t like how he is when he’s mean but I feel like if he got a handle on how he’s feeling and manages stuff he’d be better. I’ve tried to give him this advice but he barely listens to me and refuses to see someone. It’s like one moment he’s good and seems happy and the next day he’ll be tired and depressed. I don’t want to lose him over this. It’s hard because I’m 18 and I’m basically the only one who fully knows what’s going on in his head. I need advice on what to do...