"
Close the door, lose the key
Leave my heart on the mat for me
I was yours eternally
There’s an end to infinity
To infinity
Is time to get your stuff out of her fancy apartment forget about her, because she has done so. "Leave the key" - basically leave quietly you don't want to do make a big deal about it, and just leave the love she gave you and had for you at the door because yes she was yours "Until Death Do us Apart" but there's an End to those words, and sadly there's and end to the Love she thought will last until Infinity.