Brittney Griner Proposes to Girlfriend with Massive Ring!!

WNBA superstar Brittney Griner just proposed to her longtime girlfriend with a fat ring ... and she said YES!!

The Phoenix Mercury center shared the news of her engagement to Cherelle Watson on social media on Thursday, saying "I will never forget the first time I said I love you and I will never forget when you said YES!"

"My best friend, my lover, my partner in life. I love you."

Griner and Watson -- who met as students at Baylor back in the day -- have been dating for years and have been pretty much inseparable ever since.

Griner added, "I’m so lucky to have you in my life forever. You never gave up on me even when I gave up on myself. You have pull me from the ashes and held me up when I…