Billy Loomis, Rose Armitage, And 15 More Of The Worst Romantic Partners In Horror Movie History

20th Century Fox / courtesy Everett Collection

The Fly is really just a cautionary tale about what happens when you let jealousy get the better of you. Seth has no reason to think Veronica is cheating on him, but he still lets his concerns lead him to get drunk and essentially experiment on himself, leading to his fly-ification. Turning into a fly does nothing for his personality, and as he transforms, he becomes aggressive, inhuman, and unhinged, to the point that he tries to force Veronica (who's now pregnant) to fuse with him in the teleporter. Ultimately, he uses his last shred of humanity to ask her to kill him, which is clearly for the best.