The actual problem, to be blunt, was this: your relationship was based on a pretense. You have every right to be upset, even irate, about this. But before you curse them out or call names, stop and think for a minute. Ask yourself that one simple question: why would someone lie to you about his or her sexual orientation?
Generally, the answer boils down to one of two possibilities. One, they were genuinely unsure of their preferences; or two, he or she felt the need for "straight" camouflage. In the former, the lie was unintentional. There’s not much either of you could have done to avoid the outcome. And to a certain extent, this person liked you enough as a human being to find out if things would work... and actually, that's the whole point of dating.
Try to be grateful about the breakup, which in the long run saves you from any additional heartache. Breaking up is hard no matter what... and is only made more difficult when one of you has the added challenge of coming out of the closet.