Clear communication has been the biggest deterrent in their relationship. As for trust, they do trust each other partially, depending on kind of situation or topic. The difference I see in the accusations levelled related to infidelity by them is that Virat has given enough reason to Sai to believe in it, though things have changed, Sai is refusing to acknowledge that and going by her past impressions. But in Sai’s case, Virat is jumping to conclusions impulsively and being vulnerable to instigation due to his insecurities