Hell, my dad used to say outright that he hated gay people, but after I came out he's actually been trying to change his way of thinking and be supportive. Not all homophobic parents jump the gun and disown their kids. It's made clear throughout the book that both sets of parents love their sons unconditionally, and again the main character's parents were already a bit more open-minded because of his lesbian aunt.
It makes me sad to see people who haven't even read the book ripping on it. The author is an old man who spent his entire life in denial about being gay, the book's conclusion is optimistic because he's giving the characters a chance at a life he never got to live. It's a hopeful ending, which is exactly what gay teens (the target demographic) need.