Future and Blac Chyna -- What Part of 'We're Together' Don't You Understand? (PHOTO)

Future and Blac Chyna were definitely together Friday night in D.C., and it's pretty clear now they've hooked up.

Future had a concert at Echo Stage ... then went to his after-party where Chyna was right by his side.

We're told they were there for around an hour ... never apart.

Future and Chyna left together at 4 AM.

'Nuff proof?