NBA's Jeff Withey's Engaged to Playmate GF Who Busted Him for Cheating

Talk about turning things around ... the NBA player who was called out by his hot Playmate girlfriend on Instagram for allegedly cheating on her ... is now engaged!

You know the story ... 2014 Playboy Playmate of the Year, Kennedy Summers, hijacked Jeff Withey's account back in June and posted a "gotcha" style message -- saying she caught him lying to her.

"I cheated on this girl. I told my girlfriend I was going to the movies alone last night and then she found this receipt. I also shouldn't have given her my Instagram password like a dumbass."

She also posted pics of the movie ticket receipts. Oops.

But somehow, Withey got himself OUT of the dog house -- and yesterday, the Utah Jazz player proposed to Summers with a massive diamond ring.

She said yes!

Withey (we think it was Withey) went to his Instagram and wrote, "Through thick and thin, you're my best friend @misskennedys I love you. Can't wait to spend my life with you. #engaged."

Congrats -- don't screw it up.