Don’t sign a mutual consent divorce. The divorce by mutual consent is an agreement and free consent of parties are mandatory. Your husband is trying to obtain your consent through coercion or blackmailing. This type of consent is not a free consent as required under Section 13-B of the Hindu Marriage Act (HMA).
Recording of whatsapp conversation has no legal value
Your husband thinks that he will take your consent by threatening to reveal your conversation. Therefore, he has recorded your whatsapp conversation. But he does not know that that conversation has no legal value. If he reveals those conversations he will get nothing. Thus you should not take it seriously. Let him reveal them.
You are performing your matrimonial obligations and living with him in the matrimonial home. Your husband has no grounds to take divorce. Section 13 of HMA enumerates some grounds for divorce. Cruelty, desertion, unsound mind, mental disorder, venereal disease are some ground upon which the husband can seek divorce. Recording of whatsapp conversation does not prove any of those grounds for divorce.
Cruelty and desertion are based upon guilt theory. Unless and until your husband proves your guilt he cannot take divorce. The conversation between you and your mother does not prove cruelty. This is a general wear and tear of matrimonial life. The court will not give any weightage to that whatsapp conversation recorded by your husband.
File a civil suit
You should watch his activity and be ready to take appropriate action at the appropriate time. If he is planning to marry his colleague you should immediately file a civil suit for injunction. If you file that civil suit your husband again cannot seek divorce because he is the guilty party. He is attempting to commit offence of bigamy.
Your husband is a guilty party thus he cannot avail any matrimonial remedy. Recording of whatsapp chat is a mere threat therefore, you should ignore it.