The singer was spotted arriving at her hubby's rental in Brentwood Wednesday after his kid's graduation ceremony -- and it looks like it was a family affair, 'cause she wasn't rolling solo ... we're told Ben's ex-wife Jennifer Garner was also in attendance.

No sign of any of the kids, but ya gotta figure they were there too ... and like we said, J Lo joined the party -- hanging around until about 10 PM, when she was photographed leaving.

In other words ... there was no sleepover with her hubby, which kinda jibes with what we saw earlier in the day at the actual ceremony itself -- where Ben and Jen seemed to be keeping their distance, arriving with separate parties.

We'll say this ... while Jen ended up leaving Ben's place with a driver later on that night, she didn't look all that glum -- in fact, you could argue she was somewhat radiating on her way out.

As you know ... Ben and Jen have been sending somewhat mixed messages on the state of their relationship -- but the writing on the wall seems to suggest they're headed for Splitsville ... especially now that we know they're trying to sell their $60 million marital home.

Ben has ditched his wedding ring on a couple of occasions too ... but Jen's remained steadfast, continuing to wear her rare green diamond engagement ring while out and about.

Considering their storied history as Bennifer ... the fact they appear to be growing apart has kicked up a lot of chatter among their respective fans.