Nothing about what he wants or doesn't plan to do with his body reflects whether or not he'll want *you*; there are lesbian trans women, and genderqueer people who are attracted to women, etc. However, you do need to find out for sure whether he actively cannot enjoy a partner who doesn't match his porn desires, or it's just that he has some tastes in porn that aren't *required* in real life.
But with that out of the way... you're not attracted to or interested in dating a woman. If he's planning to take this journey past the point where you can see him as anything *but* a woman (because, again, not everyone chooses to make all the same transition changes), then heartbreakingly, there isn't much hope for this relationship. Similarly, if he can't have a relationship with a woman who doesn't have a penis, that sounds like a dealbreaker as well. Still, those are both big "buts," and it's not guaranteed yet.
It sounds like your biggest issue right now is that he's not being honest with you, both about what he wants to do and whom he's talking to, along with the fact that he won't let YOU have a support system for this. If you can't get him to communicate and to respect your definitions of cheating, then what you're afraid of for the future is moot - the present is already a major problem. 🙁
Good luck.