Is it normal part of growing up for a guy to get super pessimistic and depressed when he is in his early 20s?

I just have to know…. is this just a phase or something? I have been with my boyfriend for 4+ years and it feels like he has just been getting worse with his pessimism and depression since he was 20. When he was 18, he was not like that. Now it’s like, he can’t be optimistic about anything. Not his future, not his physical health, not us, not his friends, not school, not family, not his potential career…. NOTHING. Everything and anything is worthless and pointless and I just can’t take it anymore. I love him so much, that’s why I have been with him this long, but I have to know… is this going to end?

Guys…. do you remember going through this when you were younger???? ):