Look I am fully aware that Theon just did a shitty shitty thing there
But those shots were not just for scenic effect
Seeing others cut up, or in the process of being tortured, clearly brought back memories of the deep trauma Ramsay inflicted upon him
Theon may be weak and cowardly, and to an extent he has always been that way
But he is also a deeply deeply traumatised man, and it’s very very clear that to him Euron is not just a terrifying uncle - Euron is another Ramsay, another person to torture torture torture him.
So he flees. Is it cowardly? Yes. Can I blame him? No. I can’t.