"Happy birthday to the most precious angel on earth! You’re my favorite person that ever existed :) I love you sm," Davidson wrote alongside a snap of him giving Grande -- clad in a black mini-dress -- a piggyback ride.
In another post, which shows the couple hugging and gazing lovingly at each other, the 24-year-old comedian continued the compliments, writing in the caption: "One more for the queen. Words can’t express what a real f**king treasure this one is."
On Monday night, Grande also gushed over her guy. "I have no wish I have everything I ever wanted hi," she wrote on top of a pic of Davidson that she posted to her Instagram Story.
A source recently told ET that the pop star has been "dreaming" up the details of her wedding day since she was a teenager.
"Ariana has talked about marriage since she was 15," the source said. "During her teen years, she was always very dreamy about a wedding and she used to call friends and talk about one day having that one special person."
The source continued: "Ariana also spoke about a winter wedding, which seemed a little cold, but she loves the idea of a winter wonderland-type scene. We used to laugh about her fun ideas of a snowy wedding day."