Issues with Halsin romance is most likely due to a bug in coding logic anyway, there's no check in Halsin's coding after skinnydipping scene which suggests that some of his comments and behavior is just a result from a bug
Maybe the banter is a bug but I still think doing the Drow twins scene with her that Halsin should not invite himself in it should be you who initiates it and if they want to keep the absolutely inappropriate nature of him inviting himself then at the very least she should not disapprove of you declining him and shouldn't tell you about her fantasies about him unless you accept. Or just don't say anything about fantasies at all that would be much preferable. And I doubt the Drow twins stuff is simply a bug.
