I have an experience that is relevant to this. It is a long story.
In 2008, I was near the end of my senior year of college when I started a relationship with a younger girl who was a freshman at the time (I was 20, very young for a graduating senior, and she was 19). I had not been in a committed monogamous relationship throughout all of college, choosing instead to lead a polyamorous lifestyle. When I entered a relationship with her, I explained this to her, and we agreed that if either of us ever felt the strong desire to open the relationship up, we'd at least talk about it.
After a month of being together, I took her to a rave and we both candyflipped for the first time. We had an unbelievable time and I decided that she should come to Burning Man with me (I had attended Burning Man for the first time in 2007 and I was planning on going again). I convinced her to go to Burning Man with me (not hard). I was also planning to travel to Hawaii after Burning Man, whereas she was going to go back to school, so we knew that after the festival, we'd be parting ways for at least several months. We planned all summer for Burning Man to be a sort of last hurrah for our summer together, after which we would wish each other well and go our separate ways.
At a Compression party (pre-Burning Man event centered around preparing for the festival) in July of that year, I was the only member of the group that we were going to the festival with who was NOT present, because I had a family event to attend the same weekend. I found out from a friend a couple weeks after the party that she had hooked up with one of our future campmates while they were both spun out on a heavy candyflip. I wasn't particularly bothered by the fact that it had happened, but I was curious to know why she hadn't told me, so I asked. She became very upset and explained that she didn't want to hurt me and she was ashamed of what she did and afraid that it would make me angry. I explained that her honesty meant more to me than her mistakes, and that next time I just wanted her to ask me first if it was OK. She had been under the impression that I was friends with the guy she'd hooked up with, and that we all had a mutual understanding that it was OK. In reality I had never met him (and I did not meet him until Burning Man actually happened). I decided not to let it bother me and went on with our relationship as if nothing had happened.
At Burning Man, after a week of craziness, me and her had saved our acid tolerance for the night the Man burned. I took 3 hits and she took 2 and we started tripping watching the Man burn. We then went back to camp and had earthshattering sex. Like, I mean completely insane peaking-on-acid divine-archetypes-merging-in-holy-ecstacy type all-out fucking. I had never had sex that good in my entire life. It profoundly affected me.
We were still tripping pretty hard when we got out of the tent, and I decided to go dance, while she hung out next to the dance floor. She happened to run into our campmate who she'd hooked up with once back in July. After a little while of hanging out with him (he was rolling that night), she came up to me and explained that he was having a lackluster night, and that since I had already clearly had all my sexual needs met that night and was having a great time dancing (and this was absolutely true), she wanted my permission to brighten him up a bit by taking him aside somewhere and (I assumed) making out with him a bit, giving him some sort of small sexual favor, that sort of thing. I balked, and she promised not to have sex with him as a concession to the fact that I was her primary partner, the man she came home to. I figured it would be OK as long as it was clear that I was more important than he was, and told her it was OK.
15 minutes later I started getting antsy and realized I'd made a mistake. 30 minutes later I started to get really upset. At 45 minutes, I was absolutely furious with her and I was convinced that she had utterly broken her promise. As it turns out, I was right. When I confronted her later that night, she completely fell apart and confessed that she had in fact had sex with him, as well as several other things. We were both in REALLY bad shape at this point, because we were confronted with the seemingly self-evident fact that she was, in reality, a terrible person who had blatantly lied to the person who mattered most to her in the world at that point in time. She was convinced of it and she could not stop beating herself up about it ... and as much as I didn't want to believe it, it seemed obviously true.
Then something happened in my head, something she said somehow got through to me, and I realized what had really happened. What I had been afraid of the whole time was that she had lied to me about how she felt about me, and about who she was, and that instead of being this wonderful person, she was a selfish, dishonest brat who had lied to me about what she wanted so I would give her permission to cheat. What I realized is that she had actually done what she had done FOR HIM, and that she still did love me, and had seen that I didn't need any more love from her that night but that someone else did, so she had asked permission from me to try to make the world a better place by showing someone else what a truly loving sexual encounter was like. That kind of dedication spoke to me, and I felt that I'd never known someone so wonderful as her. It was like she was a young, inexperienced nymph who was only just starting to understand how to help the world with her sexuality, and I just happened to be there to see her make her first mistake in pursuit of this ultimately pure mission.
Anyway, that was effectively the end of our relationship, but it was the best end it could've had. We both came away from the relationship feeling as if we'd learned an immense amount about ourselves, and feeling that we were better people for it. We're still good friends, although we're not in touch very much anymore.
We were ALL spun out as shit for the entire episode, obviously. It could never have happened without LSD. And I'm really lucky that I was open-minded enough to see it differently in the end. It could've been terribly, unendingly shitty, and I'm certain that it would've been for most guys. I just happened to be mentally and emotionally flexible enough to let it completely change my worldview and my view on sex altogether.
Now I recognize my emotional limits a bit more, and I'm in a more strictly monogamous relationship with a different girl. I'd never make the same choices in my current relationship, nor do I think I'd ever be faced with them in the first place. But at Burning Man '08 I definitely got a taste of a completely new way of thinking about sex, and it only happened because I was tripping balls.
![:\](https://bluelight.org/xf/BL_Images/Orig_Emoji/wrygrin.gif "wry grin :\")
, I wouldn't trangress certain boundaries. 
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