The Restless Sex

Stephanie (Steve) is a restless and adventurous young woman. She is in love with Jim, her foster brother and childhood sweetheart.
Stephanie behaves childlike
Stephanie, still a child, was becoming something else very rapidly. But still she remained childlike enough to idolize Jim Cleland and to show it, without reserve. And though he really found her excellent company, amusing and diverting, her somewhat persistent and dog-like devotion embarrassed and bored him sometimes. He was at that age. Later, Jim leaves for Paris to become an author. You have to read this more to know what happened later.
Stephanie is restless
But now, Stephanie also finds herself attracted to an art student Oswald Grismer. Young Grismer, in Jim's hearing, commenting upon a similar devotion inflicted on himself by a girl, characterized her as "too damn pleasant"—a brutal yet graphic summary.
And for a while the offensive phrase stuck in Jim's memory, though always chivalrously repudiated as applying to Stephanie. Yet, the poor girl certainly bored him at times, so blind her devotion, so pitiful her desire to please, so eager her heart of a child for the comradeship denied her in the dreadful years of solitude and fear.
Jim and Grismer’s attitude
For a year or two the affair lay that way between these two; the school-boy's interest in the little girl was the interest of polite responsibility; consideration for misfortune, toleration for her sex, with added allowance for her extreme youth. This was the boy's attitude.
Jim Cleland and Oswald Grismer did not visit each other, although friendly enough at Cambridge.
Climax
In this period, Steve and Oswald decide to marry each other. When Jim finds out, he returns home to win Steve over.