Keeping in mind that I didn't follow the most acceptable guidelines for transition...
I always knew that I wanted to be a girl but I never wanted to be Transsexual..... anything but that! I saw how TS's were portrayed in the media and wanted no part of it. I hid behind other issues like social anxiety and depression, blaming them for my inability to feel comfortable with myself. I started hormones on my own, without a Dr's supervision, to try and make myself more comfortable while still trying to be the "best man I could be." EPIC FAIL !!!
What the hormones did was make me even more certain of what I really was inside. After 2 1/2 years, the results were getting really obvious... what started out as a desperate attempt at relieving depression ended up as the unscheduled start of my transition. Now 5 years in and ready for GRS, my only regret is that I didn't do this years ago! Living full time wasn't a "test" at all for me.. it felt so natural... Finally the interface through which I interacted with the world matched my mindset. I felt like I HAD to transition..... or I couldn't go on living as male.
Anyway, I think that, at this point in your life, if you're questioning whether or not you're Transsexual, the fact that you're questioning is a good indicator that you may not be so. You could also be Transgendered but not necessarily a candidate for full transition or GRS. It could be argued that "true" transsexuality is pretty near a medical emergency.. Untreated, lots of us are deeply depressed, suicidal and deeply troubled with our gender identity. Have you ever felt this way? If you were told that you had no choice but to keep on living the way you are, would you be OK with that?
You talked about the way you felt with a straight guy.... Something I realized in the TS dating scene is that there's no shortage of guys who consider themselves straight who want to date a pre-op T-Girl. What they're really looking for is a way to fulfill their gay or bisexual needs without having to admit to themselves that they're not straight. The way you felt as the more passive or submissive person in the relationship doesn't make you trans, it just means that you prefer the more passive role. That role is present in all types of relationships. It's really the way you feel in the ABSENCE of a relationship that points toward your gender identity.
At any rate, keep exploring here and with your therapist... BTW, if you want a therapist that specializes in gender but can't find one locally, there are gender therapists that will meet with you once in person and conduct subsequent sessions by phone, all the way up to hormone and GRS approvals. Here's one in Pittsfield, Mass:
http://www.affirmativecounseling.net/ This is just one of many but do seek out a specialist else you might have to educate your therapist in gender issues.

BTW, ANY therapist or psychologist that tells you that gender identity OR homosexuality is a, "lifestyle choice," should be told to go back to school and outed for their lack of professionalism. Medicine is NO place for religion-based hogwash.
You'll figure it out

and groups like this one will be here for you either way.