Here is an extreme example to prove this. I can say that I am a chair, and I can argue this until I'm blue in the face, but that won't change the fact that others will think that I am a human, not a chair. More relevant to the conversation, let's say I am a man that only has relationships with other men. I can call myself straight all I want, but if I tell other people about my behavior, they will categorize that behavior by the behavior(homosexual), thus it will not always align with the categorization that I apply to myself(straight). Okay or not, it is human nature to behave this way.
I know this is quite a bit, but the main point I'm trying to make is that there is nuance in this conversation. Categorizations aren't always evil(though they can be), and are important social signals in our society.
As for deciding “what that makes me”, I was trying to obliquely save room for the case another poster brought up, namely being gay or bisexual.