It's really just poor writing of him. Halsin could have had SO much potential being one of the more level headed and caring "good aligned" characters. Instead he seems to have just been turned into this walking sex joke.
Don't get me wrong I immediately liked Halsin and how sweet he seemed to be at first, I do like the funny stuff like the bear scene because it truly made me laugh so hard and of course like every other character there is the sex part. BUT I've heard the whole creepy thing about him which sucks as well as his horrid abandon you ending which has really ruined a lot of my enjoyment this play through since I wanted to finish end game with him. (I personally may be playing in a way where I don't really see him interact with anyone besides me so he doesn't feel creepy in my save so my experience with that is minimal).
Maybe that's the point. Halsin became popular as a character for basically superficial reasons. So Larian created a character that was just as superficial as his fan base. Honestly if you step back it's quite funny.
Jaheira on the other hand is WAY more interesting and has so much more dialogue and interactions with you if you pick her up in Act 3 and keep her on board she is amazing, and her lines are both funny and endearing. Honestly I would have loved to romance her, but with the maturity of age I realize her value is not in that she looks amazing for being almost 150 years old - but that she is an incredible friend, brave, deeply caring, and ardent-hearted. She is the opposite of the Druid Himbo...I mean Halsin.
Although MY Jaheira is Monk/Thief and crushes the enemy while breaking into every vault in the city.
Jaheira is actually the best. I love her so much in this game ( and the other two, that I want to cosplay her at a fantasy convention here in Germany next year.
I wouldn't blame his fanbase per se- there are a lot of horny people but there are also the people, who want him as a serious companion. And I mean, there are a lot of very horny people demanding Minthara as a companion, like the guy, who writes under every patch, that he wants more sex with Minthara, but according to the feedback, she turned out decent for what she supposed to be: an evil paladin, working through her issues.
About Halsin and Astarion: I think the difference is, that Astarion actually works through his trauma and can succeed and become a better person. It is the opposite of what Halsin does: making a fetish out if his trauma (according to what I read here, I'm not planning on romancing him ever).
