Разделенная радость - двойная радость

We are much happier if other people enjoy good time with us. See Горе на двоих - полгоря, радость на двоих - две радости (Г)

Cf: Happiness is not perfect until it is shared (Am.). Joy shared is joy doubled (Br.). Joys shared with others are more enjoyed (Br.). A joy that's shared is a joy made double (Am.). A pleasure shared is a pleasure doubled (Br.). A thing is the bigger of being shared (Br.)