Hmm, do you recall the specific dialogue you used *before* the party? Either flirty dialogue isn't showing for me, or it's just not very obviously flirty.
I suspect the key one is during the Weave scene when you can opt to lean into the intimate nature of the moment (can’t recollect the exact text) and then picture a kiss. The only other flirty line I can recall is saying “like your handsome self” early on when he asks how he looks. Could be more that I don’t remember, and I’m not sure whether any of them are hard prerequisites of the romance. I suspect the first isn’t, because it requires success summoning the Weave.