That's what I want to mod - you apparently HAVE to be in a M/F relationship, Tonks' quest doesn't affect it in anyway. Should be a simple flag to change, if I could only find it.
I don't actually know. Only saw her during my Mary Sue / Hermione playthrough, and the devs confirmed it only works for M/F couples when I asked why I couldn't continue the quest chain even though Hermione was railing Mary daily.