Well done for accepting yourself just the way you are and dare to be open about it!
I believe you confuse 2 different things here though. For example, what if a man is straight but still doesn't enjoy casual sex? That would lead him to have no sex during his single years but when he is in a relationship with a woman he would express his high sex drive by having sex much more often than casual-sex people. Is he a demisexual then? Same thing with a woman. Is she a demisexual because i.e she is too scared of STDs or because she is strongly religious and supports monogamy? I'd say they are just monogamous.
You don't really need to find a label that fits all the aspects of your sexual preferences. At most I'd say you are bisexual, and obviously a bisexual person will likely not mind it if a man became a woman and vice versa. (Unless one doesnt like "fake", which is an entirely different subject).
Also, apparenly one can't be 100% gay or 100% straight and there are levels, according to the Kinsey Scale: "It is a fundamental of taxonomy that nature rarely deals with discrete categories."
Well yeah, there's always shades of grey when it comes to orientation. Or really ANY facet of human existence. There is simply way too many unique personalities and way too many factors for their to be a strict 100% certainty.
From what my friend explained to me about my post, after I posted this. You can be both Demisexual and another orientation. Demisexual just means that you don't get sexually attracted to someone unless you have romantic ties to them. So one can say, be both Demisexual and Straight. Demisexual just a middle ground between sexual and asexual. It doesn't have anything to do with monogamy though. Someone can be demisexual, bisexual, and polyamorous at the same time.
So in my case, I guess the proper thing for me to say is. I'm Panromantic, which means I can get romantically and emotionally invested in anyone, gender doesn't matter, and I'm also Demisexual.