Arg, misread your original post as Alexia+Mary, somehow. Though luckily this means that I can do more than guess wildly, because that's actually one that can be a bit troublesome to proc so I have notes for myself. Doesn't require Alexia being on an NTR path.Ty for replying. I tried on Jezeera ntr path and the got mary/other guy cgs to spawn, just never got liurial. Also i made sure that the 3some with Rowan+Liurial had happened. Not sure if there is another requirement missing
But it does require Alexia to have less than 61 corruption. (Plus obviously that they had the threesome with Rowan before.) And it can be tough to be under 61 since the earlier threesome scene requires either 30 Alexia corruption or for her to have been "unfaithful." I forget if that flag gets triggered for her having threesomes with X’zaratl/Greyhide and Rowan, but if it's triggered by her doing things with Jezera/Andras you run the risk of raising her corruption up, which means no Liurial scene. I'd assume that's what happened to you.
You can lower her corruption via the console. If you don't know how to enable it or any of the commands, there are details (And the Alexia corruption command) in the linked post in my sig. If you're not interested in using console commands, restarting and trying to keep Alexia's corruption lower (But not too low) is the best bet.