For any person who is in the described situation: if you find someone attractive who happens to be MTF trans, then it doesn't really say anything about you, if you're a straight/cis man. The individual is intentionally trying to pass as female (because that's what's comfortable/appropriate for them) and you "fell for it", or more appropriately, you were convinced by it. They succeeded in their efforts to present themselves as female. That's it.

When you find out that, maybe they had a penis, or perhaps they still do, and that's a turn off for you, it changes nothing about who you are or what you like. This is what we like to call a "sexual preference". Your sexual preference is entirely your choice. Whatever you like in a partner is your preference. The reasons why you like that in a partner, may be bigoted, but simply having a preference does not, and should not, say anything about you or what you stand for.

You like what you like.

How you react when you "find out the truth" will absolutely speak volumes about your character.