I think the story is certainly plausible. Especially the way the other guy (sorry, I forget characters' names quickly, and it was months since I read it :P) keeps changing his looks partly for the main character to notice him and partly to mirror his own thoughts. The other guy could only guess why he was being ignored by his bestfriend and his compensations for it were believable as well as heartbreaking.
It's like at first it was: "Hey, talk to me", then "Notice me, I exist", then finally "I give up, go play with your cool friends" :P
Ignoring someone is kinda self-reinforcing. First you ignore him for several days. Then you feel uneasy talking to him again, so you go on not talking to him for weeks. Then you realize how awkward it would be to talk to him again after weeks of silence, so it goes on for months. Then, finally, both of you wouldn't even know when to start, so definitely years.
I know six girls in high school who made their own clique. Then it fell apart rather messily (I think it was about boys LOL). And they only spoke the barest civil words to each other for 1 and a half year. LOL. Then at our senior year, they had a heart to heart talk and they ended up crying and saying sorry and stuff. Corny, yeah. :P But... y'know... they're girls LOL. Their ignoring each other wasn't even that noticeable to us and even the teachers, but sometimes you get this undercurrent of coldness when you hear them talking to each other. So, see... it does happen in real life.
And, last but not the least, the main character was not only avoiding the other guy, but also HIMSELF. He was still in denial to the fact that he might be gay, that's why he avoided the object of his (umm... waxing poetic here LOL) 'illicit desires'. In those circumstances, ignoring would not only be to avoid the other person but also a sort of self-defense. I would say, the story is both believable and well written.