Right now my boyfriend and I are in this type of arrangement. It kind of started as a method for him to "lock in" a girl for a threesome arrangement, and by "lock in" he can sleep with her once in an attempt to lure her into a threesome with me. It then slowly transpired to allow him to have solo sex with girls he talks to if she doesn't agree to the threesome. I trust him enough to make the threesome goal a priority but sometimes I feel that he doesn't push it enough, and the solo sex is casually in the back of his mind as a safety net and therefore solo sex is inevitable and will happen.
And that's fine. He's young. He can get all the women he wants. In his last relationship he was allowed to have solo sex whenever his ex was busy, and I guess its the competitive side in me that I want to allow him to do the same. It didn't sit well with me at all when we first started but again, he had a taste of free reign and he loved it. And to me, why take away something he loved when he already knows how good it is.
Within us, he's allowed to take girls on dates and go the full mile as if he's single and/or tell the girl he is single. While for me I'm allowed to act like I'm single but only to women. Yeah I can have sex with other women but with a guy I am completely committed to my bf and not interested. I only had solo sex with a girl once but throughout my adventure with Tinder, it's always been trying to get the girl for threesome. Threesome, threesome, threesome. Again, with him, it is a threesome --- but solo sex will be there and he'll take it if she says no to the threesome.
I can say that I am happy while doing this, but jealousy does creep up and thats the downfall of this. I'd want to be informed but I don't want to the details. I force myself to hear limited things:
"Yeah her and I talk pretty much everyday"
"We do send pictures but nothing sexual -- it can get there"
He uses an S5 and it has gotten to the point where if she texts him and he turns on his phone and see's the notification, he would purposely hide the phone away and swipe the message notification away and wouldn't let me see it. He would also text her while hiding the phone away. He does this to not make me jealous and I completely understand that. It's such a grey area because he doesn't like me snooping and putting myself in a vulnerable position to get upset that he wrote ";) you're such a cutie hun".
When I truly think of this type of a relationship with him, it is healthy but to a point. We laid down some major ground rules and I hope can decrease this level of jealousy. I forgot to mention that we've only started this whole ordeal less than 7 months ago. Still ironing out the details/rules and I'm obsessively reading /r/polamory to help with some insecurities I have.