I honestly don't know how Tess'd do with ONE partner, let alone two. 
Let me explain something about Tessa. In her entire life (which, admittedly, is only 24 years or so), she's NEVER seen a loving couple up close, never seen a healthy relationship.
At this point in her life, she's just...it's an understood conclusion in her mind that "true love" like in the songs Rael sings is something for other people, not for her. Which is why she can blow off the advances of Mercuriel. 
As for Beldin-the only reason she hasn't shied off from him is because he treats her like another fighter. (Which means, in her mind, she thinks he's being friendly, not flirty, because why would he flirt with her when he clearly appreciates her skill. She really does have no idea about all this stuff. *grin*)
In short, I think Tessa'd be #Team Beltha (Team Bardin?
) because it wouldn't occur to her that such a thing would be possible for her.
I never said she understood nuance at all. 