I definitely learned that one first hand, but I've had a few threesomes since then. The fateful one was with the first girl I met on SA, which I've recounted here before. Apparently she soured on me after I made her and her bff eat cum from each others' pussies, which ruined their lifelong friendship. It was worth it.
Since then, the ongoing thing I had with a fitness instructor from SA has yielded a few threesomes, always with girls she finds. Her relationship with each of those girls has soured over time, but she keeps offering to find more girls to join us, so who am I to complain? Unfortunately, she's been less available lately, and it seems from a little social media stalking that she's gotten engaged. I'm going to see her for the first time in several months soon. I wonder if she'll disclose that she got engaged. It'll probably be my last hurrah with her, as she's approaching 30, and I've now got regulars who are 19, 23, and 24, all of whom are insatiable. The 19 year old needs a bit of coaching to help her come into her own, but she's an eager student. ;-)