How do I get my boyfriend to trust and talk to me more?

-He's a great guy but he doesn't trust me with his feelings. Like he never opens up and tells me how he's feeling so I have no idea what he's going through. He always keeps everything hidden and buries it deep inside of him and he drinks away his problems instead of talking about them. I always tell him how I'm feeling or if I'm stressed about something and he offers great advice and really I feel better just by telling him and talking about it. I want to be able to do the same thing to him cause he's a highly stressed person. But whenever I ask him to talk about what's stressing him out he either says "it's nothing" or "you wouldn't understand"! How do I get him to open up to me? We've been dating 5 months so I think by now he should know that he can trust me with anything like I trust him.Ask him very direct questions about his feelings(when I say very direct, I mean very direct)that's how I got my friend to trust me...or, you will have to wait, he will gain trust in you with time.