Worst? Not really. Selfish? Yeah, but so were the others. Did he hurt Dorothy most? ABSOLUTELY (maybe excluding the piece of shit father). (Dorothy's selfishness: never letting go of Theo although he obviously didn't want to be with her, always hated or forced herself to hate Ray in place of their father and ultimately took the throne. Ethan's selfishness: never letting go of Dorothy and guiding her to the wrong path, which was too much for her to bear because she is actually kind and Ethan can be cruel so he didn't see the problem)
You have to remember that Ethan has a "terminal illness" and he found out the best way for him to survive. (So many isekais are based on the same idea) Although he didn't want to hurt her, he prioritized his own life. I honestly can't fault him for that. He had a true love with the og FL, so to hear that the love of your life found a cure for you & got murdered while bringing it, would fuck up anyone. I too with a limited lifespan would want hurt the bastard that did it in the most effective way. Sadly it had to be through Dorothy.
Now I thought that one of the reasons why Theo in the past got angry at Dorothy for killing Ray was because they were good friends, but if I understood the bit messy translations correctly Theo had already planned on killing Ray?? For power? For his cure? I don't really get that part. But that really lowered his value in my eyes.
Spoiler
I wish Theon had gone the aide to Ray route since the start (which he will end up going in this timeline). It would have been a more efficient way of being near Ray and without misleading Dorothy. But alas it didn't happen. Maybe it wad Dorothy who asked for Theon's hand in the first timeline and he just went along with it for survival ? (I don't remember this part clearly). Anyway I agree that all the leads including Dorothy are twisted in different ways, Ethan in the first timeline brought the worst out of her, we can see it the flashback that Ethan was the one who planted to idea of becoming the Empress in her. He also killed off the pink haired girl too without letting Dorothy know, so he most probably did a lot of underhanded shit in the first timeline (lol he still does underhanded stuff like how he messed with the red head kids Dorothy took in to get rid of them and Theon's Hankerchief, all due to his jealousy). Still despite his flaws Ethan still might be the best match for Dorothy in this timeline because Dorothy of this timeline has matured a lot, she has learned to let go of her expectations of love from people who won't love her properly like her father and Theon and she has also become a lot more clear headed. Dorothy of this timeliness could truly become an amazing Empress, and someone like Ethan who is great at politics (at least Ethan who actually listens to her lol) could be a great help.
so Theon was literally the worst, most selfish asshole? And Ethan the best? <3<3