Demi Lovato engaged to Wilmer Valderrama? 'X-Factor' songstress and 'That 70s Show' actor back together, Tiffany engagement ring proposal?

Demi Lovato and Wilmer Valderrama have "secretly" been dating on-and-off again for awhile now. And just last month, the former "That 70s Show" actor was spotted buying an expensive ring at a Tiffany & Co. jewelry store in Pasadena, CA. Allegedly engraved on the bling was the sweet message "with you and by you always," Valderrama's "special phrase" for Lovato! Will he pop the big question soon?

According to RadarOnline, the "X-Factor" songstress and Valderrama rekindled their relationship over the summer. The duo even celebrated Lovato's 21st birthday together in Disneyland:

@WValderrama: "I've been so proud of the strength & commitment you've gained 4 life, keep inspiring us all! Happy birthday my @ddlovato! With & by u always."

They've been on several casual dates ever since, especially in the fall. For example:

@itsohsodemi: "Wilmer and Demi got spotted at Starbucks - 1st November."

And on November 20, one insider recalled seeing Valderrama picking-up what looked like a Tiffanys engagment ring in California.

"It looked like an engagement ring, but could have just been a nice expensive ring he was giving to Demi," the source reveals. "He was really low-key at the store and was trying to stay under the radar."

Engraved on the ring was the couple's cute, special message "with you and by you always" (the same thing Valderrama tweeted back in August).

Lovato and Valderrama are keeping things romantic during the holiday season. The "Heart Attack" songstress was named guest of honor and cover girl at NYLON magazine's issue launch party in West Hollywood on December 5. Valderrama accompanied her to the event - they didn't leave together, but they sure got cozy throughout the evening.

Then on Dec. 15, they were spotted together at a lovely United4Good brunch. And on Dec. 18, following "The X-Factor" finale, 21-year-old Lovato headed to her 33-year-old beau's private celebrity dinner party at RivaBella in West Hollywood.

So, will Valderrama pop the big question in the New Year?