This is how I think it's played. I hope it's correct.
For the walkdown bit I suggest that you play an open A-chord using one finger so 
that you can hit the G# note on the bass e-string in the A/G# chord

A (x02220@1)                      F#m (244222@1)           C#mNothing (x13321@4)like a memory to open up a broken heart
G (320003@1)                              F#m (244222@1)              EIts (022100@1)been years but i look at you now and we're torn apart

A (x02220@1)                    F#m (244222@1)                C#mNothing (x13321@4)like a face to take you back to the time
G (320003@1)                              F#m (244222@1)               EWhen (022100@1)it was you and i against the world just you and i

D (xx0232@1)                               EAnd (022100@1)i wish it hadn't happened to us
A (x02220@1)         A/G# (402220@1)         F#mYou (244222@1)fell in love with that girl
D (xx0232@1)                               EAnd (022100@1)i wish it hadn't happened to us
A (x02220@1)         A/G# (402220@1)         F#mYou (244222@1)fell in love with that girl
D (xx0232@1)                    EAnd (022100@1)i wish it wasn't true
A (x02220@1)                A/G# (402220@1)        F#mBut (244222@1)all you cared about was the girl
G (320003@1)    F#m (244222@1)    E (022100@1)Nothing like a lover to set you up for a fall
You're feeling you're ready to die like you lost it all
Nothing like you and i in that place in time
And it's so hard letting you go 'cause you're still on my mind

And i wish it hadn't happened 
But you fell in love with that girl
I wish it never happened to us
You fell in love with that girl
And i wish it wasn't true
But all you cared about was the girl