My boyfriend had a medical emergency and went to the er after dropping me at the train station

And I hurt him by not being very overtly sympathetic

But

He then hid this for the last week until I came back

How can I trust when he's nice, now that I know that he can do this?

Dump him.
He does not get to demand emotional labor from you.

it's not that clear cut

I'm just worried about trusting him and I have to think about it for a few days