The letters, which total more than 60, date back to 1949 when Taylor was just 17 years old and engaged to marry Pawley, the 22-year-old son of a former ambassador to Brazil.
"I've never known this kind of love before — it's so perfect and complete — and mature," Taylor wrote to Pawley on May 6, 1949. "I've never loved anyone in my life before one third as much as I love you — and I never will (well, as far as that goes — I'll never love anyone else — period)."
Taylor died last week at 79, an actress famous for her eight marriages as much as her acclaimed film performances.
The letters, some of which were written on pink paper in purple ink, also discuss Taylor's films, her worry about her weight, and her high school exams.
Pawley, who lives in Florida, sold the letters two years ago to RR Auctions of Amherst, N.H.
At the time of the letters, Taylor was publicly linked to football player Glenn Davis. But less than eight months after the last letter to Pawley in October 1949, Taylor married hotel heir Conrad Nicholson Hilton. The online auction, to be held May 19-26, will also include correspondence from Taylor's mother to Pawley after the end of their engagement.
The letters were estimated to be worth between $25,000 and $35,000 before Taylor's death, according to auction house spokesman Bobby Livingston. Livingston now believes the letters could fetch double or triple as much.