So, the elephant in the room...
The night that Ethan fucked Jess absolutely silly on my bed while I lay there, cowering, wearing one of her tiny pink thongs was actually a turning point. It was also eye-opening, giving me a better insight into Jess and the dynamic that our relationship had evolved into.
I hid in shame, embarrassed by the confusing erection that was stiffening by the second inside of my girlfriend's panties. Jess came exuberantly, followed by Ethan (without pulling out); he gave me another hard spank that stung my butt and snapped so loudly it rang in my ears a bit, and then left to go to bed.
The night had just begun in Jess' mind though. Without losing a beat, she started groping me, taking great joy that her other man's handprint was still visible on my ass cheek.
After a few seconds of her pawing at my hips, I reluctantly flipped over, exposing a full (though small) boner still trapped under the tiny patch of pink fabric. This set Jess off, and she started rubbing her face on it before pulling it out of its panty prison and mounting me.
I didn't last long, I'll admit, but Jess couldn't stop moaning. I don't know if I'd ever heard her this turned on while we were fucking. It was very possibly the best sex we'd had in an otherwise still pretty good sex life up til this point.
That night kickstarted a feedback loop in our relationship. I didn't inherently love being emasculated so much by my girlfriend or being cucked by her thick-cocked fuckbuddy, but these things turned Jess on so much and gave her so much giddy glee.
I started to indulge her more because that happiness would spill back and lead to more and better sex for me, and honestly I loved the extra attention I was getting from Jess when I would give in to her requests.
I started to wear her panties more often, and it ignited a Pavlovian response in Jess. Knowing I had women's underwear on would get her so horny that it practically guaranteed great sex, and often within minutes of pulling them on, if she was around to see it.
Within a couple of weeks, I think I was wearing Jess' underwear more often than my own, and usually with very little goading from Jess, or even without needing to be asked at all. The girlier the panties, I had learned, the more of a reaction I'd get from her; pink and purple, polka-dots, anything lacy, and as small as possible were best.
Jess would try to push things as far as possible, but I tried to keep this mostly private between us for now. She had also been so turned on by any even tangentially sexual interactions between Ethan and I, and wanted more. I had no plans to give in and touch Ethan's cock in any way in the immediate future.
Outside of that, Jess and Ethan were also getting more comfortable just overtly messing around in the apartment and in front of me. I don't know if this was a part of Jess' fetish for humiliating me, or just the taboo surrounding their sex just getting eroded more and more over time.
For instance, one evening, I came back to the apartment to see them huddled on the couch watching a movie together. Ethan had his cock pulled out of his pants, thick as all hell and at full length, and Jess was cuddled up beside him with the last fifth of the massive cock in her mouth.
They stayed there, watching the movie, her suckling on his cock seemingly almost more out of comfort than for any sexual reason, and barely seemed to react to me entering the apartment. I sat there with them awkwardly watching the rest of the movie, her mouth not leaving his member until the end credits.
Another time, I was at our kitchen table doing some work on my laptop while they were in Ethan's room doing exactly what I thought they were probably doing. Ethan's bedroom door opened and my eyes were drawn instinctively to see him walking out carrying Jess bent forward in front of him, his muscular arms flexed and his large hands holding her up by her hips.
They were both fully nude, and it took a couple of seconds for me to realize that Ethan wasn't just holding up Jess in front of him - he was still inside of her.
"Hey, look at this!" Ethan called over to me. He was laughing, and thought this was hilarious. It definitely gave me the normal pangs of shame and humiliation, but it was almost endearing that he wanted to include me in this, and genuinely thought it would be a funny thing to show me.
In practice though, seeing Jess also giggling while trying to supress the surges of pleasure that came as Ethan's massive cock shifted inside of her with every step he took as he easily carried around my girlfriend couldn't have been more emasculating.
He walked up to within a few feet of me, and Jess was now close enough to even be able to reach out and touch me. He then started to move Jess' hips so that he was lightly pumping his thick dick in and out of her.
That was when Jess, being held off the ground by two hands and a large cock, her face a couple feet from mine, couldn't hold back the floodgates any longer, and despite her hard work trying to supress it, started to cum.
I had been around her getting off without me before, and even with Ethan a few times, but I'd never stared straight into her face head-on while another man gave her a very hearty orgasm. She moaned and squealed in a way she never had with me.
Then, when the orgasm had passed and a rush of contentment flowed through her, Ethan turned around walked her back to his room. Jess continued with low moaning as I watched Ethan's round muscular ass walk her back behind closed doors to continue with their Olympic-level fucking.
In the weeks after the big turning point in our apartment, our whole dynamic started to leak outward in different ways, and was no longer something that stayed just between the three of us.
Jess' friend Lara was over at the apartment one day. I had left the two of them to catch up by heading to our bedroom, but I hadn't closed the door all the way. I wasn't trying to purposely spy on them, but when they were talking and I could vaguely hear it through the crack in the door, I started to pay more attention out of curiosity. To be fair, I didn't expect the conversation to take the turn that it appeared to be taking.
"It's HUGE," Jess murmurred, exasperated. Immediately I knew what the topic of conversation was. "SO thick."