Being a Christian myself, I understand some of the apparent conflicts between what the Bible says and what psychology teaches us. I also know that some Christian counselors are more traditional and fundamental than others, and those who are more traditional and fundamental are more likely to view the thoughts and feelings themselves as wrong or sinful. That makes it impossible to work through these kinds of issues because the only solution is prayer and repentance for thoughts and feelings. Contemporary Christian counselors, on the other hand, recognize thoughts and feelings as being different than behaviors. I think if your T is more moderate or contemporary in her beliefs, then you can talk to her about your thoughts and feelings because she can separate them from your actions.
As for your sister... well, any number of things could have happened in her therapy, none of which may happen in yours. Maybe she realized in therapy that she had been married to a man just because it was the acceptable thing to do, and after therapy she felt more confident in herself and no longer wanted to do what she was expected to do regardless of her feelings and desires. I don't know what happened or how it happened, but it doesn't mean it will happen to you.