Bi-sexual?

Hi, I am from a little quiet town in Arizona. Yesterday was a rather eventual day. My fifteen year old step-son decided to tell his mom that he is bi-sexual, which of course led to lot of yelling and crying. My husband was called, which later told me and he may not be disowning my step-son, but both he and his ex-wife(the boys' mom) pretty much have told my step-son that cann't change him, but that he is ruining a lot of lives by doing this, including his own. I am very open when it comes to sexuality and although I know that fifteen is to young to know, I rather know than find him dead later from stress. Anyway, when I got home I began to search the boy's room looking for something that would put my mind at ease. I don't believe people can be bi-sexual forever, it is just an escape in my eyes. I found a notebook, his journal, where he mentions a lot of boys name and how he finally told a boy he liked him, whom is gay. He constantly talks about finding some of this boys hot, sexy, and so forth;however, he talks about a girl who he thinks is hot and sexy, too. My step-son has always made ME doubt his sexuality, but I NEVER thought this could be true. I confronted him and he tried to lie to me by telling me that it was only that one guy he said he liked, but I told him I found his journal and read it, unlike mom and dad I offered my support ALWAYS. Now he tells me that he is not gay that he only said because people thought he was last year before his voice changed over to a more masculine voice. He tells me that he will change back to who he was, but I just don't see how, when he himself have told his friends that he is bi. Also, his journal sounds so true, it was for him to read and no one else, so why would he write it. I am confused, I want to help him, yet I don't know how. How can change over and tell his friends that he is not interested in boys, if he writes that stuff down and tells boys that he likes them. How can somebody say that they are bi-sexual just because people are making fun of you. I think that there is more to this, than he wants to say. In regards to his mom and dad they don't want to mention this again, nor do I believe that they will trust him again no matter what he says, but one thing is for sure they don't care to find out how, they pretty much have told him that he is ruining everybody's life. What if after hearing this he hides in the closest once more? What if he really does like boys? I 've asked him if he needs help, but he refuses. HELP, I FEEL THAT I AM AT A LOSS. NOW THAT HIS FRIENDS ALL KNOW, HOW CAN THEY BELIEVE THAT HE DOESN'T LIKE BOYS AND HE WAS LYING FOR THE LAST SIX MONTHS OR SO? THANK YOU 15 & CONFUSED