Sexuality and why it doesn’t make sense

So ever since I discovered that trans people exist as a kid, sexuality stopped making sense to me. Like for example say you’re only attracted to one gender and your partner is that certain gender. You love your pratner a lot and they love you too but one day they find out that they’re trans and they want to transition (correct me if that’s not how that works). You’re not gonna leave them because they want to transition are you? You fell in love with them because of their personality right? And if you do leave them because they want to transition were you really in love with them in the first place? So that’s why I think saying that you only love certain genders doesn’t make sense. In my opinion I think sexuality works more like types. Like someone saying they like girls with blonde hair doesn’t mean they only like girls with blonde hair. That’s just their preferred type of girl. You get what i mean. Although a big reason of why I don’t get sexuality might be because I’m bi. I don’t know dude. Tell me what you think.