If a person is "pure and selfless", it does not mean that he or she can't become jealous. I just think Tanya wants to move on, take the marriage forward. All these Yuv/Trish run-ins remind her that Yuv hasn't moved on, noone has. Just a thought.
Tanya knew of the arrangement, but I think even going into it, she thought they would be together forever (by definition of marriage) and that Yuv had foregone Trish. Tanya was saddened by it. But you know, she has people telling her and Yuv they're "perfect together" at the restaurant, etc. That sort of stuff stays with you.