If you've sifted through tons and tons of crappy yaoi, you've seen this trope over and over again.
I think this is the only one of this trope that I actually really like.
There are things that bother me, of course... And for a straight guy to legitimately fall for another man requires a lot more build-up than a single tankoubon would allow. Not to mention I cringe at girly-looking uke that cry during sex. The manga does acknowledge that gay sex requires more preparation than front-door sex, but it seems to forget it later on, as Matsuno doesn't seem to have any problems. That, and there's very little reason for Matsuno to fall for Rin. Oh, and the bonus sidestory with the animal ears was ridiculous and asinine.
On the other hand, considering the page-limit, it was still told more realistically than most crappy yaoi manga, so I have to give it credit there. To give notice to HIV risks.
The seme doesn't seem to conveniently pop out of nowhere to save the uke. The seme doesn't give him everything without making Rin work for it. He goes out of his way to help Rin get a job, and get health insurance. Rin's homophobic dad doesn't magically have a change of heart.
And to the first commenter--so one of them's straight--so what? Mangaka usually don't make characters straight in BL manga because they don't want to believe there are people who cannot be attracted to women (hello, Rin's gay), they make him straight because they think it's romantic that love can overcome gender differences (or lack thereof) or preferences. Most people aren't 100% straight or gay. Exceptions happen more often than you think. The problem is that straight people tend to be fickle--and the important thing is to make sure it's not an illusion.
Also, confirms my suspicion of the adoption = marriage for some gay couples. For some reason, I find that really moe...
So I consider this flawed, but the best of its trope that I know of or remember. (On a different topic, I wanted to bring up another interesting hustler character--Hunter from Queer as Folk was a male prostitute who started living that lifestyle from being coerced into it by his mother. He's HIV+ and is eventually adopted by Ben (also HIV+) and Michael. Hunter turns out to be straight when he falls for a girl in his class, surprisingly. Ben and Michael got married in Canada, btw. I yearn for more realistic gay portrayals in BL manga. Then again, there'll never be a show like QAF again... sob...)
Also, as someone who is actually pansexual, I wanted to note to the previous commenter that Matsuno is NOT pansexual. = _= He is mostly straight. Just because he is in love with a guy, he's still straight--at most bi. Ok? Don't misuse terms you don't understand.