Very deep and emotional feelings for a Pro Domme has happened to me multiple times and I have no problem sharing the experiences but it has also never been a purely unrequited experience for me so it may not be applicable to the situation you are asking about.

Domme #1 was someone local to me and is the reason I will no longer visit local Pros because it is too intense and overwhelming without the natural limit that distance brings. We both felt (and still feel) deeply for each other but for a lot of complex personal reasons on both sides of the fence it never transitioned into anything beyond a friendship outside of the dungeon. It "ended" when she abruptly retired for personal reasons then moved to another state about a year later. We still keep in touch (I am invited to her wedding) and she will always own a piece of my heart but we never actually were romantically involved while sessioning together for three years and I was desperate in many ways for that to happen.

Domme #2 was a touring Pro Domme who I met and had the most amazing chemistry with (and still do even after a ridiculous number of sessions over the past 10 years or so). Because of this chemistry, we decided to take it to another level at a certain point and I spent time in more personal service to her for a day or two at a time where we had a chance to get to know each other and things were going great and I really thought this was the first Domme that I might be willing to actually dedicate myself to in a real way (I am very poly in my approach to relationships, both D/s and vanilla). Unfortunately, over time, I came to understand her approach to real time subs in a lifestyle context and it REALLY didn't mesh with how I need to be treated in a relationship (we didn't have an actual problem, it was just very clear that as great as our play styles meshed and how much I like her as a person, she truly feels subs are to be treated as unworthy slaves as part of her existence and that is just not me). Since that time, we have moved back into a pure Pro/client relationship and have a great time when we get together but that realization of our chemistry not translating into anything "real" was incredibly painful.

Domme #3 was also a touring Pro and our relationship deepened when I started hosting her on her trips to Detroit. Through multiple visits we basically transitioned from Pro/client to a semi-lifestyle relationship but not really a dating one. At one point when she was in between romantic relationships we had a general conversation about what she expects from her boyfriend/Alpha but again my poly approach conflicted with her requiring monogamy so it was just obvious that to even discuss dating was pointless (not that she was necessarily offering). There is no doubt that I still love her and I have been a supportive force in her life through multiple major life events of hers but because of both of us being hard-headed about our "life rules", we basically broke off our relationship after 5 years or so and that was ridiculously painful. Today, she still knows she can count on me because she still owns a piece of my heart and we do talk/text every so often even though the breakup was about 18 months ago.

Domme #4 is something that is currently sprouting in my life and we will see where it goes. I met her when she toured into Detroit a little over a year ago and we had a great time. Again, we sort of just fit together and she started to allow me to stay with her and personally serve her when she visits (or if I go visit her). We have even spoken very seriously about visiting other cities together although we have yet to actually do it. Although we are not actually "dating", she does count on me for emotional support at times in ways that most women would ask of a boyfriend rather than just maintaining the aura that Pros have with their clients. On my side of the fence, I have definitely fallen for her as both a Domme and a person. What happens and where it will go, I have no idea.

Those are my experiences and at times there was a good deal of emotional pain and rejection involved even with the feelings being returned to me but I cannot say I regret any of them (and I am at a very good place with all of these women whether we are currently still together or not). To be clear, these are not the only Pro Dommes I have ever seen, care about or done things with outside of sessions (such as having real conversations over lunch/dinner or take on tasks, both personal or kinky) but these are the ones that I have fallen for and each has allowed me beyond the normal borders of Pro/Client in one way or another.

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Edit:

I dropped one other significant D/s relationship from this list because although she is a Pro Domme, I was never directly her client (even though I met her through other Pro Dommes when I was running camera for a video shoot she was at) and I didn't want to cloud the question, but after reading through all of the other comments I think it is relevant so I wanted to tack it on.

The two of us connected in regards to D/s and as people so our relationship is one where I am both her sub and her boyfriend (she respects my polyness so my seeing other women, either D/s or vanilla, is completely within the bounds of our relationship). This has been our relationship for about 18 months and other than the normal fights that occur between women and men in romantic relationships, there has been nothing strange or wrong about it.