Yeah, I have a whole bunch of theories about all this, but I am really wondering what advice or counsel she gave you when you talked about him. Did she encourage you to pursue him? How did she treat you?
I'm just trying to understand her angle.
I thought about this over dinner and with my wee one at the playground. Sorry this is really long but you may have a different perspective from me.
I honestly assumed that I was Ne-ing the hooking up into the situation so I really tried to accept her answers as honest. Even though I kept getting weird answers that were conflicting. Maybe It is still me-please call me on it if you think so.
Here, more chronologically:
1. He and the ESTP traveled together and partied all fall. I never thought anything of it. Everyone at work assumed they were hooking up. He hit on me in January at our sales meeting. Very strange, but exceptionally sweet. He looked like a little lost child. I would have slept with him but he didnt seem to understand follow through and let me wonder off drunk. Totally tugged the Fi with the looks and gentle sweetness though. The next day the ESTP offhand says "yeah, S told me I was being more intimate with CG than him"-as she is going to meet her fiance for three days in Mexico-where she meets a cute mexican sailor.
2. I came back utterly confused. He comes in town a few weeks later. I consult with ESTP-I told her he hit on me. She said "yeah I saw that. He is just a boy though and hits on everybody." I said he was cute and would be fun to shag-was he single? Her response "You should go for it-he has a live in girlfriend of some sort but who cares??" I ask "are you guys an item?" No. She goes and spends a week with the mexican sailor.
3. I see him a month later on a trip. He pours into my space at dinner and snuggles all over me. Very sweet. Later texts "Do I need any help?" as I am in my hotel room. Right....
Next few months are some fairly playful texts. I alternate between flirting and reminding him of his accountability to his live in girlfriend. I also give him advice on how to not piss everyone off in the workplace, how to better interact with certain individuals, not get fired for sexual harassment, and how he shouldn't hit on women in the workplace.
Once we intersect at O' hare. He climbs over everyone on his plane and leaves his luggage to run twenty gates to give me a hug before I get on my plane.
A few weeks later I spend a day at a conference with him. Somewhere in here I conclude he likely has Narcissitic Personality Disorder and started avoidance tactics. I tried to catch an early flight but got stuck waiting with him. In the hall he seemed all stupid happy face goofy again as he asked if I would be waiting with him. ESTP girl delays her flight to stay with us.
4. May-He comes back in town. He tries to talk to me and give me a funny magazine with a bunny on it-an inside joke from one of the texts. It was quite funny. He is profoundly sweet. ESTP shows up and jumps in between us and puts her hand on his arm.
That afternoon I see her at hotel with her luggage going to somebody's room upstairs. I email him that night and ask him to leave me alone.
The next day he follows me around like a lost child and pretends like I didnt send him the email. I send a much meaner email.
5. May- The next week I chat with the ESTP. I explained I had to be quite mean to the boy. I explain all of the odd things he has done and that I cared for him but did not understand what he wanted. She told me I should tell his boss that he was harassing me. WTF? I again ask-I thought you guys were kind of an item? No. However if you are close friends why would you make me turn your friend in for sexual harassment?
6. Early June- He comes in town a month later-summer. We drink. He holds my hands like a human starving for affection. We dance under the stars. She was there. I learn about tert Fe and why it isnt Fi.

I email him and ask him never to touch me again as I am an emo-tard.
7.Late June-Get drunk with ESTP in LA. Tell her all the crazy shit the boy has texted me over the months and the crazy things-like the airport thing. We drunkenly text the boy. He says I am as deep as the mariatus trench. Gets pervy but totally freaks when he finds out she is there. She totally freaks when she sees what he texted. I again ask if they are an item-No.
8. July-ESTP totally freaks out when she finds out I am going to a conference he is at and she is not. Turns out he has been ignoring her for a few months. When I get back I get grilled about what we did. I said he went home to his girlfriend and kids every night but was playing well with coworkers. I did have an interesting philosophical discussion with him regarding how to best drive resource addition to pursue new RnD projects. She emails him and tells him he has been pussy whipped.
9. August-I start putting Te pressure on the boy as he is falling behind on projects. I work from home when he is in the office. I avoid him. She starts showing up in my office showing me that he called or texted her and telling me how they partied in various places. I tell her at some point that I care much for him as a friend but it is best done from a distance.
10. Sept-Me and ESTP girl are drunk in Balitimore. She starts asking me how I would handle having an open relationship with three people-one man and three women. (I had once told them both I would likely only have open relationships from a philisophical perspective). Would I get envious of the other girls? I explained it was something you accepted as part of the relationship or you shouldnt been in an open relationship. WTF? I Ne'd-was this her, the guy and his girlfriend? WTF? Did I miss something?
11. Oct-She tells me how much fun her upcoming business trip to canada with the boy will be. Over and over and over again. For two weeks she emphases this. Okay. Once there she starts complaining about her fiance texting her really obscene text messages and why would a guy do that? Odd-she had not talked to the fiance in five months and he lived in another province. I assume she may really mean the boy who does have a knack for texting.
12-Oct-He comes in town and we all go out. When she goes to the bathroom he starts telling my date (another ENTP) that I am nurturing, like the "catcher in the rye", deep and thoughtful. We converse about literature until she comes back and starts humping the umbrella pole.
While in the office, she slaps him on the butt, hangs all over him and keeps showing me his calls and text messages. I start working from home again.
13-Nov-My party where the ditch me and she hangs all over him.
I think I am caught in a sociopathic love triangle....
(I need a new job. These people make me crazier than I already am.)