It's Jennifer Garner that pushed Ben Affleck back into rehab, a source tells X17online exclusively -- and it wasn't just for HIS health, it's for the sake of the couple's kids. Apparently Jen was worried about the former couple's three children - Violet, 11; Seraphina, 8; and Samuel, 5 -- visiting with their dad in a dubious environment, so she is now requiring Ben to get treatment for substance abuse and to have a sober coach with him 24/7, a source tells us.

"Jen wants to be careful -- she wants to make sure the kids aren't exposed to anything they shouldn't be when they're at their dad's house so she told Ben he needed to check in with a therapist again to keep himself straight," the source tells us. "She wants to feel 100% confident that when the kids go to Ben's house, they're well cared for and that Ben is able to be the best dad he can be to them."

Another report out today claims Jen even has Ben drug tested before the kids visit. The National Enquirer's source says: "Jen has put her foot down and says either Ben submits to drug testing — or he can forget about seeing the kids for a sleepover."

All signs point to Ben stepping up to the plate and doing what he needs to do to be healthy and happy for his kids ... and for himself. And let's not forget his lady love Lindsay Shookus. Our source tells us Jen doesn't like Lindsay being around when the kids are visiting Ben and she's asked that Ben stick to visiting Lindsay in New York instead of having her at the actor's $22 million Brentwood bachelor pad. So far, Ben's obliging.

We caught up with Ben today after he dropped the kids off at school -- he looked a little down, a little depressed; but since the Harvey Weinstein scandal spilled over onto him, we're not surprised he's looking less than ecstatic. After commenting on Harvey; then defending himself against his own 2003 groping incident on TRL and now a new video surfacing of a sexually-charged 2004 interview, Ben's probably super stressed! Let's see if he can get out of this unscathed ... and stay on track with his therapy!