Please help me find the title and author of this book. It does not seem to be a book from the Sweet Dreams series and it's not a Cabot book. I think the cover has either 1 or 2 girls and a boy and the background is maybe a house and trees with falling autumn leaves.

All I remember of the plot is the main character is the shy younger sister who is a wonderful artist. She falls in love with her older sister's boyfriend (or just friend). The boy is really popular but he also loves to draw. The younger sister may have entered an art contest. The younger sister and boy get together in the end.