Looking for a movie... maybe this one? [spoilers]

There was a horror film I watched as a young child, and I'm wondering if it's this one. I can hardly remember any of it except that it was sort of monster movie (possibly dinosaurs or maybe aliens) and that the protagonists end up in bed together (a man and a woman) after having survived the whole ordeal when a group of people come into their room and torch the place with a flamethrower, burning them alive.

I believe that was the end of the film -- the only reason it left a lasting impression on me even decades later is that I never saw a horror film like that which killed off the very last of its protagonists in such an abrupt and unexpected sort of way.

Could it be this film?