In case anyone wants to hear it in game or keep his approval level low so that he never brings up romantic feelings, casting charm or friendship scrolls or spells on him will artificially lower it for you every time it's cast. Just make sure to stop once he hits Low Approval and you'll get to hear the disapproving snark in all its glory without him leaving the party.
Or just keep going if you want him to leave.
low approval/annoyed Halsin is so funny he's just
"I can NOT be assed to help you useless twats but FINE... I will anyway for FUCK'S sake"