expression, suru verb (irregular)
make someone happy; bring happiness to someone
A set phrase using 幸せ (happiness) + にする (to make). Used when a person or thing causes another person to become happy.
彼はいつも私を幸せにしてくれる。
He always makes me happy.
あなたの笑顔が私を幸せにする。
Your smile makes me happy.
Intransitive counterpart meaning 'to become happy'. 幸せにする is transitive and requires an object.
Compound of 幸せ (happiness) + にする (to make). The exact historical derivation is uncertain, but it is a straightforward modern expression.