"Slowly" is a song by Ann-Margret that was used in Kate's flashback at the beginning of "I Do," when she was in the hotel. Its use in the show is notable as being one of two instances where commercial (non-original) music was used in a non-diegetic way, meaning as part of the score and not heard by the characters. (The other instance being "I Shall Not Walk Alone".) "Slowly" is the second track on Ann-Margret's album On the Way Up.
Tell me you love me again but this time slowly.
'Cause you're talkin' too fast. Baby, much too fast.
Come on and squeeze me again but this time slowly.
'Cause I like your grasp but its much too fast.
They said that the love will grow together
'Cause your mine all mine.
But darling our love won't grow an inch
If you don't take your time.
Come on and kiss me again but this time slowly.
Not so fast. Make it last.
Make it last. You're talkin' too fast.
Honey, make it last, oh not so fast.
- Wikipedia - "Slowly"