Yep! Sai is not only constantly having to fend herself against insults and accusations, but she's also dealing with her own confusion over her importance in virat's life. There's far more on her plate, especially considering she's also trying to complete her education whilst managing all this emotional turmoil. Her every actions and words scream insecure, but virat toh is only concerned that sai no matter what admits that she loves him else he will ignore her and move away, he doesn't seems to care that she's confused or insecure, just he needs her admission. No matter what a third person says, for a married person it is always the words from their spouse's mouth only that can given them the assurance about what position they hold in their spouse's life. Yes I wish sai would at least doubt that maybe virat does have feelings for her, but given her already existing doubts and insecurities now coupled with virat's distant and indifferent behaviour with her, she is all the more full of doubt that he considers her as his wife.
Why should she believe the third person when he lets a particular third person interfere in his marriage to Sai and also abuse her... I dont think any wife would be fine with being attacked by husband's ex with husband being quiet or sometimes even supporting her.. Infact Sai initially tried to put Pakhi in her place by asking her to not interfere but she was hardly supported by her husband and in case they were having a fight she was rather gaslighted...