On & Off, Off & On... May I Have Instructions For This Light Switch, Please?

this flips my switch a bit.

Certain guys have had me staring at my phone literally willing them to call or text me with the weight of an anvil on my chest until they do.

Certain relationships have hit the "on" switch in my heart so fiercely they've left me close to crazy.

And then... other guys, even one's who are hot with a capital H have me thinking, "Meeh... Next please!" 

I get that this is a universal truth; that everyone has this switch, but it just has me thinking; what is it in our hard wiring as humans that causes us to be flipped on or off so instantaneously? Why can, months or even years later, simply thinking about someone make my heart pound a little faster?

(Case in point: 12th Grade boyfriend, Ben G. We went out for a month, but only on Fridays. And I still remember exactly the way the green specks eyes looked up close and the way he smelled.)

Or the opposite: Why can I be so OFF at times? When my five year long relationship finally ended, I simply said to him, in a crowded bar, "You and me... Yeah, this isn't working for me anymore" and I haven't spoken to him since. Nor do I think of him often. After my Superman/Troll date, I (quite cowardly I admit) ignored his calls and texts for a couple days; I shouldn't have, but I did. I just didn't feel the spark with him - there was no feeling of being the only two people at Tapas - quite the opposite actually, as I distinctly remember a verrrry handsome man sitting at the bar...

(Craigslist's Missed Connections have turned up nothing, unfortunately...)
And when I finally texted Superman/Troll, and told him I wouldn't be seeing him again, apologizing for my cowardice but explaining that something had simply "shut off" in terms of my connection with him, I received this text in return:

You're amazing, you are like no one I have ever met... our attraction and closeness moved at light speed, which is something I have never experienced. Please don't back away because you're scared. It's not like I'm not. Sorry, I can't give up this easily... Whatever I can do for you, me, us I am willing to do.

How the F does this thing work?

I didn't respond. I didn't agree. And it made me wonder how he could feel that way & I could feel nothing of the sort. How I could just be OFF when he was so ON. How in the past, why have I been ON and the guy was shut OFF. (Ben G.!)

BUT...
What creates that electricity?
What is it that flips that switch?
What creates that spark!?

I need to know. I want to find it! 
Its like a drug! I need that drug!

I saw it flick on in the Aussie's eyes the first moment he saw me. Knee pressed to knee by the end of the night, sitting at that bar, I was lost, I was spinning; the electricity in me had been switched "On" for the first time in a long time. On our second date, alone in a restaurant filled with people - my heart pounding & my mind racing with, "If this man is who he presents himself to be, I could very easily fall in love with him."

I know that this spark is what I am hunting for; I've said it time and time again. But now I want to figure out what is was about him, about the couple other crazy-makers, that electrified me so much. I could give you a laundry list of things I liked about these guys: highly intelligent, almost to a scientific degree. They were manly men, who took the lead - (now that sounds very macho, but that isn't what I mean) but at the same time were (for the most part) gentle with that leadership. They made me feel valued. The ones that really took my breath away made me feel valued for my brain or creativity more so than my looks, but made me feel beautiful as well. Their intelligence challenged me.
Laundry list, schmaundry list! Really, there are plenty of guys out there just like that that I have no spark with. I went out last night with someone nice and good looking and smart and tall and a gentleman and... Meeeh, next please.

It know part of it is simply human nature; that we've evolved as people to mate with the 'best' mate we can find to make strong babies, I get it. But then, no I don't. Not at all. What is it about the fact that the Aussie inherently understood that restaurant menus overwhelm me & dealt with it so that was a sign to my uterus that he'd make strong babies?! (If you know the answer to that, please tell me. I'm curious.)

Sometimes I laugh in the car  thinking to myself that the entire point of being human is to find another human to 'bump uglies' with. Its such an odd thing, sex, if you really think about it... But, I digress....

All this being said, I am quite happy being single, I just get a slight twinge when I think about the Aussie, and then compare him side by side to other people I have gone out with, or have known.

That light switch is a damn curious thing.