
Imagine if you woke up after being unconscious for a month and found out that during the month that you were unconscious your body had been hijacked. That someone had been using your body and used it to have sex with someone.
How would that make you feel? Would it feel traumatic to you? Would it make your emotions unstable? Would you probably not know how to treat the person your hijacker had been having sex with?

If an alter ego is using your body and you don't remember it then your body has been hijacked. Why are you even arguing the word choice? If you are unconscious and someone else is running your body what would you call it? Everyone, including the guide, knew the consciousness puppeting the esper's body was not the esper, but they chose to engage in sexual activity with him anyways. If he was blacked out drunk, so drunk he had no memory of it, you would say he was raped... But only if he was a bottom lol.
You're arguing semantics because you want to hate the esper. You identify with the guide because he's the main character and you refuse to see things from any other perspective.

If it was an alter ego, if he was unconscious, and if he had been hijacked this wouldn’t be a conversation. He lost his memories. If you walked around with memory lost doing shit and got your memories back would you say that YOU hijacked YOU? Dafuq? That was still fucking him. He’s him. Whether is baby him, 20 year old him or we go into the future and fuck him as a grandpa, that’s his ass. Them is his actions. It’s not an alter ego it’s him. He did not develop an alter ego. He lost his memories. Apparently he was just a piece of shit back then. I don’t care whether it’s a top or a bottom. I don’t care who’s doing the fucking I don’t care who’s getting fucked honestly, I like the top more than the bottom any day of the week. I still don’t change the fact that his actions are his own actions

You need to reread this because he didn't lose his memories. He was an entirely different person. He essentially had DID and an alter ego was puppeting his body. Except everyone knew what was happening and took advantage of him anyways. They realized that this alter ego was younger, less experienced, and easier to manipulate. So the guide manipulated him into a relationship and sex.
Of course now that the esper is woken up he has to work through his feelings. He obviously already liked the guide and just had reasons why he didn't want to pursue a relationship. Now that he knows one is already happened he's got to work through it. He probably feels violated. I know I would.

Like let’s say your ass is 20 right now and you lose your memories and think you’re 15. You’re still responsible for everything. Everything that happened at 15 when you were actually 15 everything that happened at 20 now that you’re 20. And everything that happens while you think you’re 15. And everything that’s gonna happen until you think you’re 20 again..it’s just common sense. Nobody else is responsible for that. You didn’t gain an alter ego by losing memories. No one hijacked your body. Because nobody’s in your body to hijack it. You can’t blame your actions on anyone. Now if YOU wanted to blame someone in the story you could blame the doctors. Bro should’ve got a doctors note. He was still going to work and shit. They should’ve locked his ass up if it was really that serious. If y’all wanted to keep his dick safe.
You can't just kiss people without their consent. Yes, tops also need to give consent.