Bullies rarely actually know the sexual orientation of their target when they first start tormenting. They play an evil game of verbal 'battleship'. Where the lob slurs and hurtful words hoping to get a hit.
Considering society still pretty much sees gay as a bad thing, its the easiest thing to start using as a slur. If you are straight it hurts, so you react, if you are gay it hurts, so you react.
No one likes to be called a
faggot - gay or straight. Thus as a way to cause harm its a good weapon to throw out there at it harms all.
You need to learn how to ignore the bullies or laughingly play it back at them. Become a person who is inside of the joke, not the object of the joke. Once they see you are strong enough to not be a target they usually move on to find a new target.
Another thing, these people you call friends are not friends. Modern society has used and abused the word 'friend' to the point where people are pretty much confused over what a friend really is. These are
acquaintances (at best) and you should keep your guard up around them and keep it straight in your head that these people have no real love for you regardless of your sexual orientation.
My suggestion is that you bury your head in your books. Pursue your education and use your hard work in study as the excuse why you are not dating/going out with girls.
I also suggest you take up a 'manly hobby' of some sort. Guns/hunting/mechanics/woodworking - something that stupid people think of as being a 'straight man's' hobby.
Get an interest in a 'manly thing' to throw suspicion off you. Understand homophobic societies have stereotype behaviors for homosexuals, don't be a stereotype homosexual.
Learn how to defray homophobia by pretending to be homophobic yourself. Don't go all squirrely here and join a gang who goes out to bash gays with baseball bats. But do learn to shudder when a known homophobic brings up the subject of 'The gays'. Saying "It makes me sick to even think of it." can be an honest phrase.
Granted they think you are made sick by thinking of homosexuality, truth is you are being made sick by how much pretense and issues they have with homosexuality. So you didn't lie.
The real problem here is you live in a society that is currently intolerant and may actually support gay bashing - maybe not legally, but the general majority may give consent to such by not openly showing tolerance and acceptance.
For thousands of years gays have ran from persecution, either actually moving away, or by 'hiding in plain sight'. Since you are committed to staying at this particular school (I know there is
only one college on earth that you can get your education from
its not like you can take up studies elsewhere) you are going to have to hide in plain sight.
Unless by some miracle more colleges exist, then you may want to seriously consider having your credits moved to another more accepting/tolerant college.
For the record, no one can read your mind. They can read you actions and reactions, they can read your behaviors. When someone is accusing you of being 'that way' for the intent of causing harm, its not because they really know - they are guessing - unless you have done something to make it clear that you are gay.