Sounds like Didi and Lyn got caught up in the moment, which can happen pretty often when couples want to spice things up in the bedroom. Threesomes are a way to explore who you really are and sometimes reveal unexpected dynamics.
This kind of situation happens quite a bit with couples.
If you're looking for something similar without the drama, I found a site at
https://villideitti.net. It's like a sex club where you can easily find a date just for sex, no strings attached. It might be worth checking out if you're interested.