It is not ethical at all. Being in a relationship with your girlfriend means being committed to her, and having any sort of improper relationship with her mother violates basic moral and relationship boundaries. It can also cause a great deal of harm to all parties involved, including the girlfriend who would be deeply betrayed, and the family dynamic would be severely disrupted.
The interesting aspect might be how the novel delves into the reasons behind quitting. Maybe there are complex relationships within the hero's party that drive the main character away. It could also show a different side of the hero's journey, like what happens when one steps out of the spotlight.
I'm not sure specifically as I haven't read it in full, but likely there is the main character who quits the hero's party. There may also be other members of the party who play important roles, like the leader of the party or a close friend of the protagonist.
First, you need to recognize that this is wrong and immediately stop any inappropriate behavior. Then, you should be honest with your girlfriend. It will be extremely difficult, but it's the right thing to do. She may be very hurt, but in the long run, honesty is better than hiding the truth.
The 'Chronicles of Narnia' is a great example of heros novels. The children in the story are heroes. They enter the magical world of Narnia and fight against the White Witch to save Narnia. Their adventures and the growth of their characters are really fascinating.
I'm not sure which specific 'Harem Heros' you are referring to. There could be various works with this name in different media such as books, games or anime. It would be great if you could provide more context, like is it a novel? If it's a game, what kind of game is it? Without more details, it's difficult to tell the full story.
One popular heros journey novel is 'The Lord of the Rings' by J.R.R. Tolkien. It follows Frodo's journey as he undertakes the dangerous task of destroying the One Ring. Another is 'The Odyssey' by Homer, which tells the story of Odysseus' long and arduous journey home. 'Harry Potter' series by J.K. Rowling also fits this pattern, as Harry grows from an ordinary boy to a powerful wizard while facing numerous challenges.
The apostles can also be seen in a sense as heroes in the New Testament stories. For example, Peter was a key figure. He was bold in his faith, often speaking out on behalf of Jesus. He walked on water for a moment, which showed a certain level of faith - based 'heroism' as he was willing to step out of the boat at Jesus' command. They also spread the teachings of Jesus far and wide after his death and resurrection, facing many difficulties and persecutions.
Honestly, 'a heros end hentai comic' is a rather mysterious and perhaps niche concept. It could potentially involve a story with a heroic character reaching an ending in a hentai (adult) context, but without further details, it's hard to say exactly.