It would be pathetic if Tachibana's reason to hook up with Jinguuji is "because magic means women don't it for me anymore, and you're the guy I'm least disgusted being with".
He needs to get a girlfriend, realize he (still) likes girls, but then also realize he like Jinguuji better.
The idea a gender-bent protagonist could be bisexual is the truly underused option. Basically the only ones I know of are Kanojo ni Naru Hi: Another and (repostedly) Idol Pretender.