First Orchid for Pat (Pat Marlowe Series) by Anne Emery

When Tim goes away to college, Pat is left behind to finish her last year of high school. They have decided to date others and keep their lives as normal as possible while they are separated. But Pat grows very impatient. As her senior year goes along, she finds to her own astonishment that she is growing up a little! A friend persuades her to go out for dramatics and she finds an engrossing new world. Thrilled and happy about her discoveries, Pat tries to share them with Tim. But he isn't interested. Pat is so distressed that she wonders about their future together. It is only after Pat learns that she can make choices and adjustments that she finds an answer.