Great poem! I love the imagery of the box of photos, and the way you build up quite a warm, cosy tone in the first stanza only to shatter it in the second (particularly with the line "The day you lost your sister"). My favourite line is: "We whisper through the moments".

There are only a couple of typos:

[The day they set of the alarm] - this should say "off".

[But the pasts what we know best] - this should say "past's".