Joe Jonas -- On His Own In L.A.

With the future of the Jonas Brothers in peril ... and a big decision looming ... Joe Jonas ventured out alone today -- rollin' solo in L.A.

As we've reported ... Joe, Nick and Kevin are deeply divided musically and are expected to decide the fate of the band this weekend -- whether they'll stay together ... or go their separate ways.

24-year-old Joe -- the middle brother -- hit up SoHo House in West Hollywood this afternoon ... sans brothers.

Maybe he's trying it on for size.