On the one hand, Faye's history with Sven certainly does warrant her making a quick exit stage left. She's been hurt by him and in several ways, Sven will never change.
But on the other hand;
- the bar they're in is a public place. And unless Faye was in the restroom for a long time, Sven was probably there before her. So she really can't dictate where he should be or shouldn't be.
- Sven is Dora's brother, and if he knows that she and Tai got engaged, Dora probably told him immediately, if not by calling around or by phone, hence why Sven wasn't sitting with them. If he does know, he's got just as much of a right to be there to celebrate as Faye does. And if he doesn't know, well that's just awkward.
- Faye is giving Sven way too much power. She had moved on, she had a loving relationship with Angus and she's now in a loving relationship with Bubbles. She's moved on, or at Faye thought she had.