I think the unrelated message is not a surprise at all. I assume he'll need a bite more time than a day to really think this through, and I don't think he wants to cut all contact until he actually has an answer. Then again, if you ever feel like he's taking maybe a little bit to much time, I guess it's perfectly fine to mention it again. It wouldn't be fair to just leave you hanging, without even knowing what the heck is going on. But again he probably just needs a little more time.

All in all I think you're being very very reasonable, but a little hard on yourself. It seems like you're going through a stressful time, and the need or desire for mental/emotional support is not selfish at all. We all go though tough times and it's nice to know, that there is someone you can rely on.

And you're right. It *would* be unfair, if you really *expected* him to assume this role. But that's not what you do. You're basically asking a question. 
And please don't forget: you guys being closer would have mutual benefits. It's not like you're taking advantage of him.