See... another poem dedicated to brendan. You sure he's your friend? haha i'm really curious about this guy. Anyway

When I open my (mine,)
I only think of you.
= I think it's mind? If it's mine... In my opinion it doesn't flow well.

When I (pass,)
In Heaven I only wait for you.
= My suggestion add 'away' so it's pass away.

Overall:
Well I like your other poems better. But you wrote this for someone special. (Poems that are made from the heart are always great)

I guess brendan was really happy to read this - I know coz if someone made me a poem I'll be really happy.

Keep up the good work.