i'm a terrible person.

So i have this coworker. We will call this person... Tulia, because that is their name, and Tulia has no way of ever seeing this page.

Now that we have our background information, i will proceed to write about my problem regarding Tulia.

So when i first came to work in the summertime, as the new girl of course i had to get to know everyone else, or whatever. i didn't really do that but you know, it's kind of unavoidable if you're going to be working together. it just happens.
So this guy is very friendly, hispanic, young, maybe twenty. He/She's one of those hispanic people that looks white.
Okay so now we know something is kind of weird about this person.

I didn't think anything was weird about him/her at all, actually. I never even questioned his/her gender at all until yesterday, not even in the slightest. I thought this person was obviously a male.

Well unfortunately yesterday, while i was talking to some other person, they referred to Tulia as, "she". I thought, well that's weird, but maybe it was a slip of the tongue.

The next day he continued to call this person, "her", and "she". and each time i grew a little more uneasy, because i was realizing that this was obviously going to be an issue. now that i think about it, i guess he coulldd pass as a girl... and his name is Tulia, ending in ia, which is usually a feminine characteristic. How do you ask if someone is a man or a woman? obviously i can't rely on my own natural human instincts or observations with this one because clearly i am questioning myself.
And i can't just ask someone else, i don't see that smoothing over very easily.

i've decided that there are a few options.
1) He is a man
(a) the other guy has a permanent joke and always calls tulia a girl.
(b) the other guy just accidentally keeps calling him "her"
2) He is a woman.
(a) She just looks and sounds very masculine for a woman
(b) She had a sex change.

every time i convince myself that she HAS to be a man, i'm just like well gosh.
it just doesn't add up. and i feel kind of awkward that i've been friends with this person for a few months and still don't know their gender.

i think the best i can do is just wait until he/she needs to use the restroom, and watch which one they walk into.