We caught Ben Affleck heading to his Buddhist rehab center in West Hollywood yesterday, and we were wondering what's up since we haven't seen him there since January, but an insider just gave us the full scoop!

Apparently, Jen Garner recently demanded the actor recommit himself to treatment and sobriety, after she became worried that he was slipping back into old habits. She also issued an ultimatum - stay sober or you can't see the kids!

A source tells X17:
    "Jen got back from Sweden with the kids and didn’t like what she saw with Ben. When the kids aren’t around and Lindsay’s in New York, Ben sometimes isn’t as healthy as he should be. The very next monday, Ben was back in rehab.”

The Batman star is working off a Buddhist-based philosophy of treating his addictions. The center is "the premiere Buddhist informed addiction treatment center in the United States. Our treatment program utilizes a unique blend of Buddhist philosophy and evidence-based clinical approaches, including attachment theory and EMDR therapy. As clients move through our program they gain clarity and learn to take refuge in transformational practices, supportive community, and their own potential," according to the center's website.

Maybe this is why Ben and Jen's divorce is taking so long to finalize?