It could be a rogue Death Eater who has been hiding and waiting for the right moment to strike at Harry. They might use some forbidden dark magic to seriously harm him.
Neville Longbottom would be an amazing boyfriend. He's gentle, kind - and he has a great deal of courage that he didn't even know he had at first. He's also very knowledgeable about plants, which could be really cute. For example, he could give you a bouquet of magical plants he grew himself. He's the type of person who would support you no matter what you want to do in life.
I think Harry Potter himself would be a great boyfriend. He's brave, loyal, and has a strong sense of justice. He's been through so much and still manages to keep his heart kind. He would always protect his partner and be there for them through thick and thin.
My ideal Harry Potter boyfriend would be Cedric Diggory. He's so charming and brave. In the Triwizard Tournament, he showed great courage and sportsmanship. He's also very kind-hearted, like when he helped Harry in the maze. Plus, he has that handsome, gentlemanly look that's really appealing.
One interesting story could be 'The Hogwarts Quiz Championship' in fanfiction. It has the characters competing in a quiz with really tough questions about Hogwarts history and magic spells. Another one might be 'The Great House Quiz', which focuses on questions related to the different houses and their traits.
In some fanfictions, Harry could be seriously hurt during a dark magic attack by a new and powerful dark wizard. For example, he might be hit by a powerful curse that drains his magic and leaves him in a critical condition.
You can start by searching on popular fanfiction websites like Fanfiction.net or Archive of Our Own. Use specific keywords like 'Harry Potter quiz' in the search bar. Check the ratings and reviews of the stories to see which ones are highly recommended.
I value bravery the most. In the wizarding world, there are so many dangerous situations. A brave boyfriend like Harry Potter himself would be able to face any threat and protect you. Harry faced Voldemort multiple times without hesitation, and that kind of courage is really attractive.