So, Gavin has doubts and anxiety about a reunion.

I’m glad to be back to “real” backgrounds though they take a lot more time.

There were several clues that this was a dream.
– The borders were gone (Biggest clue. The only other place this has happened in the comic is when Gavin was thinking about the jay he was following.)
– Gavin is nodding off in the first panel of the dream sequence and “wakes up” in the second.
– Diana is wearing the amulet instead of Gavin
– The background becomes more abstract as the dream takes an uncomfortable turn.
– The sudden appearance of the knife is ambiguous. Diana is never shown touching it, it’s just there suddenly.

Those are the major ones that I can think of offhand. Gavin coincidentally running into the exact person he was looking for in the middle of the woods should have also been somewhat of a give away although it could have been interpreted as a case of deus ex machina.