this seems to be a fairly common experience for some trans woman, having an attraction or obsession for a girl that you want to be with but also want to be. i have a friend who had a similar mentality in highschool but i think she's getting over it now that shes transitioning.
Thought was lot simpler than this explanation. Unless she also help him in some way i cant see how wanting to be with him as a man would be healthy for her who wants to become more of a girl.
@brunocar yeah this is kinda ironic, i hope their relationship doesn't end up like with his childhood friend tho but knowing this manga, and it's completed, I have a ride to catch on