I have been going out with, sort of "dating”, this woman for a while, about 1 year.
She has a steady boyfriend.

Anyway, we always go for lunch, at least once a week, on a somewhat secluded restaurant where it will be unlikely that any of our acquaintances will find us. We always sit side by side and discuss everything: our dreams, expectations, our childhood, etc.
Our chemistry is superb!

On the other hand, on the physical escalation side, everything has been going very slow – so far she initiates hugs with me and I always kiss her on the cheek. I grab her inner thigh; hold her in my arms occasionally, etc.

I have tried to escalate more, but she will not reciprocate – she actually freezes - sometimes she even tries to slow things down a bit.

However, she frequently looks for me, and bumps into me every now and then at our workplace – we are co-workers.

Once I told her that, whenever her boyfriend would go on a trip, that we would then have a lot of fun together (in a naughty manner). She did not say anything.

Indeed, her boyfriend went away recently for about a month. During this time however, she flaked on me twice and kind of avoided me. Immediately upon his return, however, she resumed looking for me and bumped into me at least five times during the first day I met her upon his return.

Ok, if she does not want to hook up with me, why does she constantly look for me now? And why does she agree to go out with me on quasi-romantic lunch dates?

It does not look like a classical friend zone because she is never too comfortable around me, she is even somewhat nervous at times. And also, she does not feel at ease to invite me out. Actually, whenever she wants to go out with me, she comes to me close to lunch time and lingers until I invite her out
.
Whenever she finds me, she talks, talks, and talks. When someone joins us, she waits until the person goes away and subsequently, if I allow, she then resumes talking to me.

Sometimes, rarely though, she flashes me her breasts by leaning in front of me with her unbuttoned shirt. And if she notices someone else is also peeking, then she closes herself off in a very obvious manner.

You may say I should make a move – but I tried. In such cases, she lowers her head and I end up kissing her hair. Or, she dodges my hands and arms with her body as if I was a fighter jet.

What is going on and what should I do to step up the process and smoothly close her?