Responses
I mean if he still remembers he should have not killed his father
He said it himself that if he knew he wouldn't do it
I don't think he remembers, I think Gueon senses things. Like how he can sleep with Teach, or how he is attracted to him from the get go. It was only at the end, when he was near death, that he actually either regained a memory, or he just got the feeling it would work.
He definitely also remembers his past memories. He knew that jumping off would reset. Which is why the beginning is different.