Complications can occur when your keyholder is married to someone else.

As some of you know, I am in a keyholding/chastity relationship with a wonderful friend that is married to someone else.
This has been going on for awhile now and quite successfully.  We both agreed that there would never be sex between us. And that has not changed.   This whole thing was not undertaken without serious thought and we tried to consider every possibility.  All in all I think we did a pretty good job.

We had both agreed there would be no cheating. And yes, we both meant it.  I can say for myself that I meant it heart and soul despite 'normal male tendencies' due to the fact that I value her so much, the thought of doing something to 'break' her life is anathema to me.
 But...
We have always been super close and shared our secrets with each other.  What we have come to learn though; is there are some 'secrets' that you may not even have fully realized about yourself, to yourself.
 Case in point...  We both knew she had a bit of a 'dommish' streak and had never gotten the chance to explore it.  Me preferring to be submissive to women went well with this.  It was a match made in heaven.. at least on paper.  
As the weeks went by we both learned a few things.  We had been focusing on making sure that those hard lines in the sand were never crossed.  That new emotions didn't grow between us.
What we overlooked was our sexuality evolving.  Our "I'd like to try this" evolving.
As she explored her dominant side, she realized there were other worlds drawing her attention and desire.
The same is true for me, but my desires are greatly grounded in pleasing her.
In other words, her fantasies will for the most part become mine as well.

  The root of the issue. 
She has expressed an interest in spanking, sometimes with a paddle or other device, even employing bondage.   The other 'evolution' is strapon play.  At first when this was mentioned it was tongue in cheek, playful and we'd both laugh and mock ourselves by adopting a sort of stereotyped role play.
This was always on the phone or in texting until last week.  We were moving some mattresses (volunteer work) and I was a brat and set my end down as a joke. She didn't say anything, dragged it herself the last few feet and set it down like she hadn't noticed. She went back out the door towards the truck to grab another.  I rushed over to help, thinking I might have irritated her a bit, and not wanting to exacerbate things.  I leaned forward, grabbed a hold of the edge of the box springs and started pulling. 
Suddenly, there were three firm whacks to my rear.  I can honestly say I was quite surprised considering it hadn't been whacked in a good 40 years give or take.   When we looked at each other...  Well, I don't think I can articulate all the thoughts and emotions that passed between us without a single word spoken.
 
   The Problem
What exactly constitutes cheating, or even sex for that matter?
We've began talking lightly about this... cautiously even.  It is unfamiliar territory. Unprepared for and unexpected.  The fact that we will not have intercourse, chastity or not, remains unchanged.
That, is firmly cheating in both of our minds.  But now... now we have a gray area that we didn't even know existed.

On a side note for those that may be wondering, yes I am currently locked and she found out about "Locktober" somehow. I was going to tell her about it eventually.. like in mid January..... Not sure I'm ready for this.