"I think I was attracted to him because he used to be a girl" That's gonna be a yikes from me.
I'm with Nya, this is gross. I held out this long out of curiosity but to say this mischaracterizes the queer experience would be charitable at best.
PS - the common sterotype for trans men is "just a butch lesbian" which seems to not be the case here but I'm not going to give the author too much credit
I'm lesbian, and I look at trans men, and see how feminine they are, and get attracted to that part of them. I kind of shake my head and think it's a shame because they're usually very beautiful in their feminine form. Granted I see most of them pre-transition.
Also there's a lot of queer people I know that are overly attached and overly emotional. Hell I am one of them. I'm pretty sure I'm borderline, so if I was still with my best friend, I think I would get a little crazy like Gin's high school friend. Especially if I was deeply closeted like that. Fortunately I'm not.
In the past though, I have been possessive to the point that I wanted to seriously kill or beat up my romantic rival. If they didn't live on the other side of the ocean, it could have been bad.
I've calmed down a lot, and I know such an answer is not acceptable, but I didn't care in my early twenties. I'm 30 now so... I still suffer from that deep attachment though to my best friend who stopped being friends with me 15 years ago.