Whitney Houston's Daughter Bobbi Kristina & 'Adopted Son' Kiss in Public

The Twitter posts and PDA-filled paparazzi photos have certainly raised eyebrows.

Ever since Whitney Houston's death, daughter Bobbi Kristina Brown and a man described in media reports as Bobbi's "adopted brother," Nick Gordon, seem to have something going on.

The day after Brown's interview with Oprah Winfrey aired March 11, Brown, 19, cozied up with Gordon, 22, at a Starbucks in Atlanta.

They have also been spotted out and about in the city hugging, kissing and holding hands – most recently while grabbing pizza in Atlanta on March 13. And PEOPLE has learned that they are living together in Houston's house.

The pair have apparently known each other for years. Gordon reportedly was taken in by Houston more than a decade ago and had been living with the family in her Atlanta home.

"I have always felt there was some interest beyond a platonic interest in each other," a close family friend tells PEOPLE. "It appears to me that Nippy (Houston's nickname) either didn't see it or didn't want to address it."

There is no evidence he was ever legally adopted and Houston leaves nothing to him in her will (it all goes to Bobbi Kristina).

Gordon addresses the whispers on Twitter, posting a photo of them together and telling his followers, "We're just close – just going through her mom's passing and grieving together."

"Yea we got a little closer and what!!!" he writes. "All the haters that dont know us or th real story can't un follow me."

• Reporting by LIZ McNEIL

For more on Bobbi Kristina Brown and her "adopted brother" pick up this week's issue of PEOPLE magazine, on newsstands Friday