So they both are just opening boxes without denying each other's claims. Sid in all his explanation or monologue didnt say that he and aarti didnt lied. He said about goa which rashmi didnt refuse.
Then that 9 month part where they didn't talk to each other but fir he said that kab kab kaha kaha bani bolu? And she stayed silent. And all that jab chahiye thi and sab kuch and so many instances
They both were in relationships which didn't end well or didn't ended at all(ghosting/cheating or any reason whatsoever these two are my assumptions according to their behavior and some statements) than there is arhan in the mess. She may have moved on pretty quickly (according to Sid) that's why this whole ek daal dusri daal...
They both know too much about each other and that's why none of them are coming clean and takes these cheap shots at each other.
This are strictly my opinions and can be far of the mark.