You mention that "He had been drinking for most of the night." It's not unusual for a person under the influence of alcohol to do something, or say something, which the person later regrets. He may feel he wishes he did not expose to you as much about his personal issues as he did. It's possible, I think, that he may not even know on a conscious level why he is suddenly reluctant to get together with you. You describe him as someone who keeps tight boundaries around his personal issues. It sounds like alcohol loosened those up and, now, he may not like that you know. He changed the image that you had of him so drastically that, as you say, you were "totally shocked."

Leaving the ball in his court sounds like a way of respecting his space. That doesn't mean that it would be wrong for you to call him once in a while - not too often - and say you were thinking of him and asking him how life is going and share a few details of your current life. If he seems to not want to stay on the phone with you, then it would probably be best to back off.

His reason for withdrawing from you could be this and it could be that. Trying to speculate on what goes on in another person's mind is probably futile and pointless. Even if he wanted to explain it to you, he might not fully understand, himself, though he did explicitly say he did not want to be perceived as "weak" by anyone, including you.

For him to get so emotional telling you about his depression indicates, I think, that he is not in a state of equilibrium. He has not achieved effective management of his mood disorder. That, in itself, is depressing. He might be in the midst of an exacerbation of his recurrent depression. Was he "drinking for most of the night" because it was his birthday, or has he got a substance use problem. Maybe he is in some despair about becoming well and doesn't want to be a burden to you.