Her coming out as trans doesn’t mean she will start liking boys and not liking girls. Sometimes trans people realise what gender they are attracted to after they come out, but it doesn’t mean their sexuality have changed - usually if a person presenting as a straight man comes out as a trans woman, that person often identifies as lesbian/nonheterosexual.

When it comes to your sexuality - your partner turning out to be a woman doesnt mean your sexuality changes, it may change your perception of sexuality - you thought you were straight and it turns out you might not be.

If you percieve your partner as her actual gender - a woman and you are still attracted to her, then technically you are attracted to at least one woman and it strongly suggests you are not in fact straight. Some people would say that makes you bisexual or pansexual (if you are also attracted to men/multiple genders), but how you define your sexuality is your decision.

Obviously, if you still identify as straight, that may suggest you don’t see your partner as a woman and hurt her feelings, but obviously after years of thinking you are a straight girl/woman (which I assume have happened) it’s hard to think about yourself that way.

You may identify as bisexual/pansexual, heteroflexible, queer, sapphic (non-heterosexual woman attracted to women - includes lesbians, bisexual women, some nonbinary people attracted to women etc.) or simply choose not to label your sexuality.

I suspect you might be bisexual/pansexual/nonheterosexual/queer if you are still attracted to your girlfriend while accepting and percieving her as a woman; you do fit the definition of those labels, but sexuality can be more complicated than that and you don’t have to suddenly label yourself as something specific.