Several weeks ago, I was in a chat room. I began a conversation with someone. He responded, to my surprise, that we’d chatted before.
I couldn’t place him, so he sent me a photo of him and his boyfriend.
Unfortunately, I still wasn’t sure whom I was chatting with, because it turned out I’d slept with both guys in the photo before, at different times, apparently while they were already living together.
It’s similar to this time I went over to someone’s apartment to hook up, and the guy explained to me that it was his ex-boyfriend’s apartment, and that they were now friends, and that he was staying there while the ex-boyfriend was away, and I realized I’d been in that very same apartment before, to hook up with the ex-boyfriend, before he was an ex.
It’s a small gay world, isn’t it?
Perhaps this could be called six degrees of penetration.
Now THIS should be the basis of your book. It’s a great jumping-off point. :)