Q:

Is the only way a Symbiote can truly die, by choice?

I found this image on Facebook recently.
Did Venom ever say this, and if he did, is it true?

I've included the MCU tag because I know he's in Spider-Man 3, but it's been a few years since I watched it and I refuse to watch it ever again.

A:

Venom did say it...
In Web of Spider-Man Super Special (1995), the fifth and last issue of the "Planet of the Symbiotes" arc.

But he was certainly wrong
The nature of the Symbiotes has been subject to a number of retcons, as with most things Marvel. However, in most media Venom (and other symbiotes) can die.
For example, in Spider-Man 3, Venom was killed by a Pumpkin Bomb.

And in any continuity, it seems difficult to believe that with all the cosmic entities in the Marvel Universe—the Phoenix Force, Death, the Beyonder, Eternity, Galactus, the Fulcrum and so forth—the Symbiotes are truly invulnerable to destruction.

