I do a lot of my best thinking in the shower, so I had a long shower and gave your ideas some thought.
In terms of definitions, homosexual and heterosexual are a little difficult. Both terms are used as both adjectives and nouns. Some acts are easy to classify with those adjectives. Others are more difficult. What is it if someone's hot girlfriend straps on a huge dildo and fucks him in the ass? What if a cute tgirl has complete sexual reassignment surgery and then she and I hook up? What if I don't know about the reassignment? What if she gives me head before the surgery and I don't know?
Used as nouns, the terms are even more difficult. By stating that they're non-exclusive, you seem to step right into the gray area you were determined to avoid. I'm a straight male. I'm also a little gay. What does that even mean? I haven't even touched on the ambiguities of biological outliers. What if I have sex with a hermaphrodite, but avoid contact with the penis? What if I used to have sex with a tgirl, but before and since only had female partners? What if I masturbated with my buddy when I was 12? What if he touched my penis? What if I touched his?
Language is a living thing. Meanings change over time. Some concepts are even lost completely. I think both of these terms are going through tremendous changes right now, and I think the changes in public opinion about things like pride parades and gay marriage reflect those societal and linguistic changes.
The American Psychological Association, the California Psychological Association, the American Psychiatric Association, and the National Association of Social Workers filed
this brief supporting the challenges to Proposition 8 in California and discussed the temporal and contextual nature of these issues in great detail. This is not fringe thinking. It is mainstream science.
My personal speculation is that this is all happening because we are finally departing the blindness and ignorance of Victorian Christianity. It's about fucking time.