shayam is blinded by his greed for money and his lust for Khushi. you are right only Anjali's pregency has kept Arnav from telling Anjali the truth. women in this condition can suffer shocks that can affect their health. and Arnav has already told shayam that only the baby has kept Shayam in Anjalis life, otherwise he would have removed him from her life. remember the scene on the road after the marriage.
Arnav made it very clear to Shayam. if Anjali was to loose the baby or any harm come to Anjali Arnav would only hold Shayam resposible. and though shayam says that he will tell Arnav about the accident. i believe he will not want Arnav to hear a word about it. Arnav will realise something is fishy and will start keeping an eye on shayam. which he is not doing now. as he is keeping a watch on Khushi more.
now as the truth is going to come out, things will change. i hope Arnav finds out about this incident. then Arnav and Shayam will have a faceoff.