I agree with everyone who has said that of course you can be straight and crossdress, many or most are, and I even think you can fantasize about a man while dressed and that doesn’t really change anything – you’re simply a straight crossdresser who sometimes has a harmless fantasy.
For myself, I don’t find men attractive in either male or female mode, and I consider myself a straight male. However, my wife and I have a dominant/submissive relationship, it is what underpins my crossdressing, and it extends to the bedroom. I don’t want to be too explicit, but she sometimes does with artificial equipment what a man would do with natural equipment. Does that indicate homosexuality on my part? Does the equipment matter or the person using it – in this case, a woman. Does it matter that it is at bottom (so to speak), a role play and I’m getting excitement from the scenario itself as much as the physical aspect? These might be questions to be answered by a philosopher or a sex researcher, but I find them to be a waste of time for me. I am who I am and like what I like. So does my wife. We have an unusual arrangement and an unusual sex life. What label is on it isn’t really important to us.