transwoman confused about my sexuality?

[Natalie]

i'm a 20-year-old pre-op transwoman, i've lived as a woman pretty much since the start of my high school. i no longer have any doubts or trepidations about my gender identity and i feel content and happy living as woman. i'm doing HRT right now and it's going well. It's now my sexuality that's confusing me. For a long time i felt like i was asexual. i found men physically beautiful and women looked cute to me. For the most parts, tough, i had no interest in sex. Last year, for the first time i had sex with am attractive bi guy but i couldn't feel anything. i wasn't aroused. The sex was quite disappointing and confirmed to me that i was asexual. However, a couple of weeks ago i had an unplanned sexual encounter with a ciswoman who happens to be a roommate mine and i was quite into it. i was easily aroused. The part that freaked me out however, was that what i experienced was pretty much heterosexual sex. i was in charge and enjoyed myself thoroughly. It was also one of those rare instances where i didn't feel disjointed from my genitals. i've experienced a bit of a breakdown since that encounter. i'm also a bit scared to bring this up with my therapist. i know transwomen can be lesbian and that's cool with me...but, why did i enjoy straight sexual contact so much? It's freaking me out.