In the Shukumei no Yubiwa series (宿命の指輪シリーズ), also called the "With These Rings" series:

1. Tenshi to Koi to Okumanchouja (天使と恋と億万長者; The Secret Millionaire):
   FROM SINGLE MOM TO CINDERELLA

One youthful summer night Rick Covelli captured innocent Jill Morgan's heart, then headed for Texas without her. Now the charming oilman was back. But Jill had an ironclad commitment to her child - and no intention of entrusting her fragile heart to any man ever again.

Striking it rich hadn't erased Rick's desire for the angelic beauty beyond his reach. She asked him for nothing, but he could give her the world with his secret wealth. Though he wanted to protect and provide for Jill and little Lucas, he had to resist. Because Rick was a sweet-talking adventurer, not a small-town family man...wasn't he?

2. Yurusarenai Ai (許されない愛; The Man, the Ring, the Wedding):
   TAMING THE TYCOON

Just when Angelina Covelli was about to pitch her hopes of a "forever man" into the whistling wind, along came the dreamiest bachelor. John Rossi was gorgeous, sophisticated, wealthy -- and just passing through town. Which put the dark tycoon off-limits!

Angelina was so inocent .. and utterly irresistible. But kissing was not part of the plan. His true identity secret, John intended to complete his family's vendetta against the Covellis. No matter how alluring he found sweet Angelina, John would never compromise his mission by wedding the enemy. Then again, he did have that ruby ring....

(info from fictiondb)

English version via Renta!: vol 1, vol 2