Here is another girl who works with me:

While working together, she allows me to fondle her entirely, to pet her, etc. I am able to caress her inner thighs (very close to heaven), rub her breasts, grab her butt, etc. I once fondled, caressed, and kissed her in many places (except lips) for almost 7 hours straight.
This has been going on for about a month.

Curious: she does not agree to go out with me outside of the office; and she does not like to talk about what we do (whenever I try to bring out what we do, she stops everything and starts to act normally).

Inside info: she has a boyfriend.

Today, I tried to kiss her - I did that when she turned to face me - her face close to mine.
I then touched her hair, face, and went for the kiss!

Guess what? She immediately put a sad face - a very clear microexpression of someone who would be just about to start crying. But did not move her head away.
Noticing the very sad face, I aborted my plan and kissed her in the forehead.
She immediately recomposed and, clearly appeared somewhat relieved.
And we went back to heavy petting as if nothing had happened.

Later on, we exchanged texts and she told me she does enjoy what we do, but is afraid of getting too attached.

Please help me: Why on earth did she put such an incredible microexpression of sudden deep sadness just because I was about to kiss her lips?

This is not logical - it is emotional. But what kind of emotion will lead to that?

And what should I do from now on to close the deal?

In my opinion, it looks like she sees you as an option she can have at any time. If you want something more, like a relationship, or even sex then I think you need to make yourself more exclusive and definitely strengthen your frame. It's like you're playing into her world and what she gives you and youre allowing it. You need to be more in control

Thanks for your reply.
It is interesting; however, it is also too theoretical for me.
I do not quite understand what what should I do "to become more exclusive", or to "stregthen my frame".
On more practical terms, what should I actually do to achieve all of that, and "to be more in control"?

I may not be the best one to answer, but it sounds like you need to spend less time with her. Be more mysteriousif she asks why you arent giving her enough attention, tell her that you only reciprocate attention, if she wants it, tell her to come and get it

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