Lynne
What Exactly are you so upset OVER???

His sister being an interfering bittch??? So, you knew that...
He DID'nt set this up...so I wouldn't be mad at him...disappointed...maybe for not standing up for himself to her.
Go to family dinner? Why not, his family didn't do anything...sit with ex...no...leave right after....
Would I be ticked? Depends on the relationship...casually date with bonuses...to me means not committed relationship...
So, even were the ex to show up and it not be a negative for him...it shouldn't be an issue if you are not in a real relationship...
This, tho, may push both your buttons as to WHAT you WANT FROM one another...

I Became Insane
With Horrible
Intervals of Sanity

E.A. Poe