、。
Haru-kun has always been this way. At heart, he's really a gentle person.
Literal
Haru-kun [topic-は] from-long-ago like-this is [explanation-の], heart [topic-は] really gentle is [explanation-のよ].
A woman's loving defense of Haru. 昔から ('from long ago / for a long time now') is a time-range marker. こう ('like this') refers deictically to Haru's observed behavior. 心根 ('one's inner heart, true nature') is a literary compound — 心 ('heart') + 根 ('root'). The two sentence-final のs (contracted からの and のよ) give it the soft explanatory feminine tone. The sentence argues that surface behavior doesn't reflect true character — a common Japanese interpersonal observation.