Valmiki Ramayana Kishkindha Kanda Sarga 32 Shloka 7
Original Shlokaसर्वथा सुकरं मित्रं दुष्करं परिपालनम्। अनित्यत्वाच्छ चित्तानां प्रीतिरल्पेपि भिद्यते4.32.7।।
1 source checked for this shloka
सर्वथा always, मित्रम् friend, सुकरम् easy, परिपालनम् to maintain friendship, दुष्करम् is difficult, चित्तानाम् of mind, अल्पेऽपि even on flimsy ground, प्रीतिः friendship, अनित्यत्वात् fickleness, भिद्यते will break.
'It is easy to earn a friend but keeping the friendship sustained is difficult. Due to fickleness of mind friendship gets broken even on flimsy grounds.