For me, it's obvious that a relationship with him is more sexual than based on love.
Up until they patched in the epilogue, that would have been my interpretation as well. But with the epilogue I'd say it is quite open to your own interpretation. If you don't pay the sex workers at the brothel for an orgy and say no to Mizora, there is little in the way of dialogue and reactions from Halsin to suggest that he is only in it for the sex. You have a sex scene that shows a strong sensitivity and concern for Tav's needs and camp dialogue with kisses that are very warm and caring and some playful banter about his appetite for sex and previous encounters. If someone's interpretation of that is that he is in a romantic relationship with their Tav, I think it makes logical sense and is consistent with the story they have played.
Just as if someone else played the game and started a relationship with him and one of the other origin characters, paid the sex workers for an orgy and banged Mizora and Haarlep, there is a lot of reactions and responses that would reinforce their interpretation that the relationship with Halsin is based on sex and not romantic.
Do with it what you will and what makes you happy about the story you want for your Tav.
