Ariana Grande Pens Adorable Birthday Message to 'Soulmate' Mac Miller: 'I Love You With All My Heart'

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Ariana Grande is so into Mac Miller, she can barely breathe -- and we can't get enough of their cuteness!

The "Into You" singer took to Instagram on Thursday, penning an adorably sweet message to her rapper boyfriend on his 25th birthday.

WATCH: Ariana Grande and Mac Miller Are Instagram Official!

The post was accompanied by a Snapchat video of the two jamming out in the car. Naturally, Grande used one of the app's popular face-altering filters.

"Happy birthday to my best friend for life / soulmate @larryfisherman," Grande, 23, captioned it. "I love you with all my heart."

The former Nickelodeon star and Miller have been friends since the two collaborated on her catchy 2013 track, "The Way," but didn't start dating until they reconnected last September. Since then, the pair hasn't been shy about expressing their love for each other via social media or packing on the PDA while out and about.

RELATED: Ariana Grande Shows Major PDA With Mac Miller in 'My Favorite Part' Music Video

When ET caught up with Grande a few weeks after the duo confirmed their relationship, she revealed her ideal date night with the Pittsburgh, Pennsylvania, native, and her favorite part about being in love.

"Chill, I don't know," she gushed. "Like, random adventures. Going on drives, looking for Pokémon, going to cute movies, making music."

"Every day [with Mac] is super exciting," she continued. "Just waking up and being like, 'Hell yeah!' Do you know what I mean? It's great."

It doesn't get much cuter than that!

WATCH: Ariana Grande Reveals Her Ideal Date Night -- and It Involves Pokémon

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