Can anyone suggest me a good Gay fictional novel?

For context, my brother is gay. He's recently gotten into reading and has a preference for novels with gay characters. He's gotten through a few books, in particular he enjoyed "The Song of Achilles" but didn't seem to like the other ones he had.

I'm planning to surprise him by getting him another book, do any of you have any suggestions for novels with gay main characters? Preferably in the romance genre but even if romance isn't the main gist it's okay as long as you think it's a
a good, engaging read and it's LGBT.

Thanks in advance for your recommendations!