A few thoughts:

First I wonder what is the purpose of this distinction: are you wondering what you are, for yourself, or are you wondering how to present and identify in the world to others?

Trans people often occupy fuzzy boundaries of gender, and concepts like heterosexuality don't even make sense given the science we have on sex and gender, the idea that humans can be perfectly divided into two categories has been debunked and it leaves a lot of questions about our sexual orientation concepts that are based on this system of "same sex" and "opposite sex" attraction. (For example: if a man is attracted to a non-binary intersex person, are they a gay or straight man?)

I strongly believe trans men are men, but that doesn't mean some trans men don't look, talk, or even behave like women for various reasons - it's not surprising that someone who is attracted to women might experience attraction to certain trans men (namely trans men who may look or seem like a woman, who are not passing as cis men). This is actually rather common as many trans men start with identities as lesbians before the transition. (See Stone Butch Blues for an example of the challenges some face between identifying as a butch lesbian woman or as a trans man.)

(As a side note, this kind of situation can raise problems for trans people, as a trans woman myself I find it disturbing when people are attracted to masculine traits of my body, or when they are attracted to the mixed gender traits, because I don't feel those parts of me are accurate reflections of who I am.)

All this to say, I don't really feel any surprise that a trans man might exist as an exception, his valid gender identity as a man doesn't necessarily invalidate your nearly exclusive sexual attraction to women - since what you might have been attracted to in him may not have anything to do with his masculine traits or male gender identity, and in fact have been enabled by his feminine traits and past.

I can't tell if you are avoiding acknowledging this possibility because it is politically incorrect or denies his gender identity, but I do think it's worth considering - we shouldn't be so judgemental for what is obviously true (that trans people are not always perceived as their gender identity, and that people are sometimes attracted to trans people in ways that aren't entirely validating to the trans person's gender identity).

Either way, it seems to me that for all practical reasons there is no motivation to identify as anything other than lesbian. The words are there to communicate, and when you identify as a lesbian you are communicating that you are attracted to women - and that's true! Your attraction to the trans man is exceptional, and maybe upon reflection it could lead you to realize that you have more flexibility in your sexuality than you previously realized, but that doesn't require you to identify as bisexual when the reality is that you are for all intents and purposes exclusively attracted to women ...

For comparison, I am solidly bisexual and usually identify as such, but it often feels like it doesn't communicate accurately the way I feel - which is that despite my undeniable attraction to men, I live as a lesbian and can't really imagine ever dating or being with a man. So even though I'm not strictly a homosexual, I still identify primarily as a lesbian because I think it communicates better to people what I am. I am in a long term, committed lesbian relationship and my bisexuality is a technicality.

Also, being bisexual is not necessarily absolute - there are shades of bisexuality, some people are only "incidentally" bisexual and primarily heterosexual (or primarily homosexual and only incidentally bisexual), etc. The Kinsey Scale is one tool used in academia to define sexuality on a spectrum - it has its problems, but at least it gives a way for someone to classify their bisexuality in a way that doesn't just imply equal attraction to men and women.

Anyway, I hope this helps 😅 I can't tell if any of this was what you were looking for or not, I'm sorry if it wasn't.

i knew a demisexual lady who spent a lot of time debating if she could identify as a lesbian on dating sites since it'd been years since she was attracted to a man. with someone who wasn't demi, it would be easy to say that her sexuality was fluid and changed and now she was a lesbian but before she'd been bi. but being demi meant that maybe she just hadn't connected with a dude in the right way in years.

i guess if i was in your position, I'd find some comfort in an umbrella term like queer or sapphic. a lot of people are uncomfortable with those terms, and i get that, but that would be the direction i went. i would want to give myself permission to stop thinking about it.

but, i honestly don't see a problem with you going back to identifying as a lesbian, either. if another exception pops up, now that you better understand how bpd and trauma can confuse things, revisiting the question at that future point would make sense.

figuring yourself out is a fine place to be as well. you might be someone whose experience will be coming to terms with never fully being sure. you wouldn't be alone there.