Intensive metta practice can be challenging on many levels - body, heart and mind. One of the most supportive things we can do to deepen the intention of love and kindness is to consciously and deliberately relax; truly relax in mind and body.
Friendship is necessary in life for the support of psychological and educational growth. It can equal the Dhamma or eight fold path. How to make our mind our friend, tentative exploration owith " Vitaka SanThona
Sutta" MN -19 + MN -20