This is not 100% correct im just playing it as i hear it.
This is the begining of the song with the piano playing i thought i should make a tab for it for guitar.
[ Tab from: https://www.guitartabs.cc/tabs/r/rihanna/unfaitful_tab.html ]
Intro
X2
e|-------------1----------------|-------------1---------------------------1-----------------------------|
b|------1--3-4--------1--3-4-3--|------1--3-4--------1--3-4-3------1--3-4--------1--3-1-0---------------|
g|----0-------------1-----------|----1-------------1-------------1-------------0------------------------|
d|------------------------------|-----------------------------------------------------------------------|
a|--3-------------3-------------|-----------------------------------------------------------------------|
E|------------------------------|--4-------------4-------------4-------------3--------------------------|