[SWTXBelle]

You said you joined as a sophomore a year and a half ago - how much longer do you have in school? I know everyone may not agree, but it you are only going to be active 4 more months it might not be worth the drama to come out. It depends on how much of a burden not telling would be. If you are going to be busy with classes and graduate stuff, the fraternity might not be as big of a problem as it has been in the past. Your call, of course.
If you have more than the one semester, you should most certainly tell - but you might want to talk to your advisor first. Maybe you could plan to come out (at a chapter meeting? informal meeting? - I think telling everyone at once might be the way to go) and have the advisor ready to discuss the situation with anyone who might have a problem. I would hope your brothers would be able to handle the truth manfully and in a mature fashion. Ultimately, they should focus on you as a person, and not as a sexual orientation. Everyone is giving good advice - think long and hard, and I am sure you will see the right thing to do. Best of luck, and I hope everything works out for you.