How can I comfort my boyfriend?

How do I let my bf know that it's okay for him to cry in front of me without making it a big deal?? He always comforts me when I'm sad or crying but whenever he's upset he obviously tries not to show it. A few days ago he was telling me about everything that's been stressing him out lately (family stuff, friend stuff, work, life in general) and he started tearing up a little. I tried to comfort him but he kept looking away from me and ended up dismissing everything he had said, saying he was fine and ending the conversation there. He made some excuse to leave.

He's also been worrying me recently because he seems to have a pretty low self-esteem. Like he says things like he wants to be better for me and that he doesn't know why I'm with him and not someone else. Like, I'm with you bc you're my favorite person ever... duh.

He just seems down and not as vibrant as usual. I want to be able to comfort him and make him feel better. I'm do worried about him bc of all the suicide stories I hear about and maybe I'm paranoid or something but I just want him to be happy. I'd do anything for him.