It feels to me like the comment exchange on this answer failed to point out that if her immediate answer really is/was I don't know, it's still important to ask to get her thinking about it. Whether she's thinking about admitting why or thinking about trying to figure out why doesn't really matter - so long as the question goes unasked, if she hasn't thought about that question already, she probably won't start until asked. Figuring it out can take a while, so she should be given as much time as you're comfortable giving. — Ed Grimm 1 min ago

I've also known some who would refrain from initiating the conversation for fear of admitting that they were really interested in the person. That they feared, without their restraint, they would be forever bothering their would be significant friend or maybe even other. — Ed Grimm 57 secs ago

One comment to people who might be holding back for reasons given in this answer: depending on the jurisdiction you're in, it's possible that someone in a higher position is not legally able to make moves towards a relationship, even if it's legal for them to accept moves from the other party to initiate a relationship. In areas where sexual harassment lawsuits can end careers, and the laws do not indicate a way for one to possibly approach an underling for such reasons, it can be a huge issue. — Ed Grimm 28 secs ago

4. could be taken further. I once knew someone who was very interested in a long distance relationship. But she had several local relentless suitors she did not want and work pressures that kept her from having the time to initiate conversations. Complicating matters, her suitors were coworkers and she often worked late due to work pressures. She intended to initiate conversations but thought it was important to wait a few days by which point her nuisances would have her distracted. So she was always happy to receive an email from her friend and be reminded she could throw out her suitors out. — Ed Grimm 1 min ago

I'm only just seeing this question, but for what it's worth i would have recommended using the phrase 'much appreciated', which in the UK at least is an acceptable stand alone acknowledgement. it does also avoid any fears of using emoticons seeming at all cutsey. — Spagirl 45 secs ago

Can't comment on the polyamorous community part, but avoiding having the physical-only relationship with a friend, and instead trying to hook up with someone random on a dating app, sounds like good advice to me. — AndyT 13 secs ago

Great answer-- people like to get reasons for things (or at least they often think they'll like knowing the reason), but the only relevant info here is that the OP no longer wants to pursue a romantic relationship with this person. — Upper_Case 44 secs ago

This sounds like it could be a great question for this stack exchange if it was made a bit more clear what you're asking. Some of the people here could get a sense of a question out of that, but I would guess most probably couldn't. Please edit your post to ask a definite question. "Can you help?" is not a question in this context as it does not offer any direction about what kind of help is wanted. Thank you. — Ed Grimm 1 min ago