What do you mean by a neutral relation ?
Romance needs approval from your love target. If you have made a lot of actions which have been approved by your love target then the romance trigger is enabled at the party from my experience.
As far as I know, there is no indicator of the global approval level for one character.
[edit]
Argh. I know
For some reasons, if your character have been the first to talk with Astarion, in multiplayer, Astarion will always talk to you even if your wife's character is trying to speak to him.
I have reported this as a bug to Larian.