In this instance it may not help you at all to tell him. If he is not gay, then it will only lead to heartache, as your friendship could end up ruined.
'What would you gain from telling him?' that is the question.
If he is not gay, then he will not return your feelings … Read more
If you still live at home, I wouldn't mention it. One, it's personal and two, he could make your life a living hell until you move out. If he asks you about it, you might say something. Other than that, you don't need to announce that you're bisexual. It's no one's beeswax but your own.