The 46-year-old actor was snapped dressed casually in black shorts and a hoodie, marking his first sighting since entering rehab two weeks ago. He also met up with his rumored love interest, Playboy model Shauna Sexton, as her blue car was spotted at his home. ET learned that Affleck was at home working out, but has not yet left treatment.
On Wednesday afternoon, Affleck was snapped being driven back to rehab, and he appeared to be in good spirits while looking at his phone.
Meanwhile, Affleck's estranged wife, Jennifer Garner -- who drove him to rehab on Aug. 22 -- was busy promoting her new action film Peppermint in New York City on Wednesday. The 46-year-old actress looked chic in a white sleeveless dress and nude heels while exiting the Greenwich Hotel.
A source tells ET that Garner knows Affleck met up with 22-year-old Sexton on Wednesday and is "frustrated" with the situation, given that the actor's friends have concerns about his relationship with the model.
"He had stayed in touch with Shauna the entire time he was in rehab and the people at the facility and friends had huge concerns about it because she isn't sober," the source says. "She is a huge, red flag to everyone that is trying to support Ben with his process. Shauna is giving him false confidence and that is their biggest concern."
"Jen knows he is back at the house with Shauna and she is so painfully frustrated," the source continues. "She knows he has to do this for himself."
Meanwhile, the source says Affleck is continuing to work on himself during his third stint in rehab. ET learned that Affleck is being allowed to work out a few hours a day at his home while in treatment and is always accompanied by his sober coach and therapist.
"It has been an intensive challenge but he had no choice," the source says. "For Ben this was a life-and-death situation. It was very dire and that is the main reason Jen had no choice but to get involved."
"He believes he is strong enough to venture outside the facility with sober coaches," the source adds.