Just because you came out as a gay male, doesn't mean you can't develop new feelings. People change over time. I know of many members of the queer community who first came out as gay and then came out again a few years later as bisexual. You are not alone in the feelings that you have. Most importantly, don't be afraid of how you feel and go with what is in your heart.
College is time of wonderful people and experiences.
You should only do what you are confortable doing, take your time if necessary. Coming out as bixexual, straight, pansexual, or whatever, is very much like coming out as gay. Sometimes people don't recognize that coming out as bisexual or straight after being a part of the gay community can be just as difficult as coming out as gay, but it is. But most importantly, you need to be comfortable with yourself and be happy with who you are. If coming out as something other than gay will do that, then go for it.