Mutual love; a relationship in which both people love each other (often used as a four-character idiom).
二人は長い交際の末、相思相愛で結婚した。
After a long relationship, the two married each other in mutual love.
相思相愛の関係は互いの信頼が深いことが多い。
Mutually loving relationships often have deep mutual trust.
若い頃の友人が恋人になり、ついに相思相愛になった。
A childhood friend became a lover, and finally they fell in mutual love.