Only five-and-a-half months ago, the two stepped out as a couple after meeting through friends.
At the time, he was still wed to his estranged wife, Keri (they finalized the divorce last month), but he and Simpson were never shy about taking their romance public.
They jetted off to Italy in July, where they celebrated her 30th birthday with a lot of PDA.
On her Twitter posts, she also displayed shots of them kissing.
Last month, in an interview with USA Today, she credited Johnson with bringing "out a lot of light in me."
"He definitely makes me happy and makes me very comfortable being who I am," she said. "It's nice to be with somebody who praises you for all the right reasons."
She was equally vocal about Johnson, 31, during Maria Shriver's Women's Conference last month. "I've never really been in such a healthy relationship," she said. "I'm like, 'Something's going to go wrong. Is he going to trip me or something?'"
She called Johnson "a hottie" who "has been an inspiration. He really knows himself."
Despite her declarations of love, Simpson's pals have been concerned over their romance.
After he ditched plans to attend business school in Pennsylvania, sources told Us Weekly some of her friends think he is using her for her lavish lifestyle.
He "was never that successful in the NFL, but he's always wanted the celebrity-lifestyle," one source said. "I believe that Jessica is his way to get famous. He's using her." Adds a second insider, "Eric doesn't have a job, he just follows her around. Her friends do not trust him."
Simpson has turned a blind eye to their concerns, telling USA Today she even wants a start a family soon. "[I] definitely dreamed of being married my whole life and having children, so hopefully that's in my future," she teased.
For now, they're focusing on the holidays. They'll all spend Thanksgiving in NYC for the Macy's Day Parade.
"I know his family's going to be with us on the float at the Macy's Day Parade, and my family will be there," she recently told Ryan Seacrest, adding that they all likely planned to return to her home state of Texas for Christmas.
"Having a boyfriend through the holidays, we're going to see how all that splits up," she said.