Mia Khalifa says she loooooves Houston Texans rookie Deshaun Watson ... but insists it's strictly platonic.

The ex-porn star wished the QB a happy 22nd birthday Thursday with a video of them playing mini basketball in her apartment this past June ... leaving people speculating whether they were a "thing."

But we spoke with Mia who tells us there's nothing but serious friendship goin' on ... and it all started over a home-cooked meal when Deshaun moved to H-Town.

Mia says she lives close to Watson and, with him being new to the area, she invited him to her place for some hospitality ... and they've been tight ever since. No sex though. 

Still ... good for you, Deshaun. Good for you.