Is it normal to have certain fantasies only while aroused?

I consider myself in general a straight male. I do enjoy anal/prostate stimulation in general, and employ it during sex with my girlfriend.
When I am sexually excited, I often have recurring fantasies about having sex with men, always as the receiving/submissive person, and often in the context of the "sissy/crossdressing/forced feminization" fetish (where the receiving/submissive guy is dressed and feminized like a girl, and treated as such sexually). These fantasies are incredibly exciting to me, often causing me to watch porn of the genre, order related items off the internet, and even attempt to "hook up" with men and act out these fantasies. On a few occasions I have acted out these fantasies with men, and relatively enjoyed it, until orgasming.
However, once I orgasm, it completely disappears, and I am filled with a revulsion that causes me to cancel any orders, delete any posts, rapidly end the encounter, etc. and I am a normal "straight" male mentally again.
I'm not attracted to the male body at all, even while aroused during these fantasies; just the penis specifically, and the idea of being submissive and feminized and used.

I can't figure out if I'm bisexual or have some sort of gender identity issue or what...and I don't want these fantasies to jeopardize my relationship. Is this normal?

Awaiting Votes