I can't pretend that Shadowheart is a certain way in my Shadowheart exclusive playthrough because I can't forget any of what I found out.
Look at it this way. All that there is in the game only suggests that Shadowheart is not fully monogamous, she is open for some experimenting. That doesn't mean that she is against exclusive relationship, will be unhappy in exclusive relationship or even considers your relationship not exclusive by default. In drow twins discussion she says "If you are comfortable sharing, so am I". Halsin butting in and everything else happens only after player says "Yes" to that, which indicates being comfortable with at least some sharing.
Although disapproval if you refuse Halsin doesn't make sense and has to go. It also doesn't make sense and has to go for Astarion too while we are on it.
