"The way he came into the store, the mood he was in, I knew this was very serious," Arabo tells PEOPLE exclusively. "He said 'Jacob, I'm in love. This is what I want to do.' "
Though there's been no official confirmation of a wedding, the pair obtained a marriage license on the Caribbean island of Eleuthera, and Cannon's family confirmed the pair got hitched.
According to Arabo, Cannon, 27, came to Jacob & Co. two weeks ago and asked to have an engagement ring created for Carey, 39. "He said he wanted something in pink, so he picked something in a light purple-ish pink. He was very involved and he trusted me to design the ring."
Despite the couple's whirlwind romance, Arabo said: "He loves her. That's all I know."
As for their compatibility, he added, "[Nick] is an artist, she's an artist, so they have a lot in common. He was very, very happy. Happier than I have ever seen him. I've known him four or five years and this was a really happy moment for him, in his life."
17 Carat LoveOn Thursday, Jacob & Co. confirmed to PEOPLE that the ring he made was crafted from platinum and features a square, emerald-cut fancy light pink diamond in the center, surrounded by 58 intense pink diamonds, flanked by two half-moon diamonds. The total carat weight of the ring – the center stone alone is 10 carats – is a jaw-dropping 17 carats, with a value of $2.5 million.
Though some speculated that Carey's ring was the same one Cannon gave to his former fiancée, Victoria's Secret model Seltia Ebanks, Ebanks's ring was 12 carats and made of colorless diamonds.
"It may look similar from afar but it's not the same," said Arabo. "I would never do one of the same he had before."