Are you attracted to men, or not? Liking anal has nothing to do with your sexual orientation, lots of straight guys like anal, lots of gay guys don't like it. Are you aroused by the idea of a woman having anal sex with you, or a man? What matters for sexual orientation isn't the activity, it's the partner.
This being said, yes, orientation can change to some extent over time. Hasn't happened to me but it does seem to happen to some people.