The Dictionary of Sexology definition really doesn't mean anything to me. Neither does Webster 1913's. So I took a crack at the modern, online Merriam-Webster and found this:

the quality or state of being sexual
a : the condition of having sex
b : sexual activity
c : expression of sexual receptivity or interest, especially when excessive

And so I was relieved, because people are using it incorrectly. "Sexuality" does not mean the same thing as "sexual orientation" or "sexual preference." It doesn't describe who you like to have sex with; it describes how much you like to have it.

This grammar lesson was brought to you by
the anal-retentive English teacher who lives in my forebrain.
Thank you.