As per precap I think, either Yash read Arti dairy...misunderstood her that she is doing all good things to him and kids just for MIL wish or to create good image in front of family.
OR most possible thing is...DHOKHA in Yash's POV would be...Arti married her for her kid Ansh..thinking that he needs father. Yash married Arti for his babies..thinking that they needs mother. BUT they (Arti-Yash) will not have any husband-wife relation...BUT he comes to know that Arti loving him madly and now he to falling for her...so in that way they both doing injustice to their respective EXs and Arti made Yash to forgot Arpita...that the reason is he behaving wired.😳