Sam Asghari posted a PDA-filled montage of him and Brit Saturday for International Kissing Day. As you might imagine, they pucker up quite a bit in the extended clip.

There's a lot of sweet moments here -- Sam and Britney working out together, being silly on camera, and even dancing ... which ends, of course, with a peck on her cheek.

It's clear Sam is thinking about Britney -- who he's been dating since at least 2016 -- as she receives treatment for her mental health ... especially since she isn't with him at the moment.

TMZ broke the story ... Britney checked herself in to a live-in facility at the end of March because she was incredibly distraught over her father's ongoing ailments after multiple procedures. She'll be staying there until the end of this month.

Britney's dad, Jamie Spears, underwent 2 surgeries to deal with issues related to his intestines and colon. Britney's been caring for him while he's on the mend ... she even canceled her new Vegas residency because of it. At the time, she apologized to her fans in explaining the decision.