What the hell changed? I was mainly asexual until I met her...? Also, what do I do???????

So, I (15F) have a girlfriend Amy (17F). But I'm polyamorous so I'm also talking to another girl Elizabeth (15F). I started talking to Elizabeth after a mutual friend introduced me to her and we're getting to know each other and find out if we like each other. We also are gonna video call and plan to meet up.

However, Elizabeth is also a trans girl so Dad won't let me see her if he knows she's trans, so I have to say she's a boy (she uses any pronouns, so...) and I will just use her more masculine/gender-neutral name "Alex".

Also, how do I have sex with her, because I'm curious, without getting pregnant and having my family know what's going on?

Elizabeth is also really freaky, us being teens and all, and I feel like she's changing me with her views on sex and all. My mutual friend of hers said she would definitely fuck me if we met up and started dating, and like I said, I am curious. I just don't understand what happened to turn me from mainly asexual/ace spectrum to really horny for this person.

I will not be impulsive and just get to know her more but DAMN. She (or the picture she sent of me) is also CUTE???