Thank you for your question during what is no doubt a very trying time in your life. Please forgive my directness, bottom line, if he really wants out, you can slow him down to maybe 6 months or a year or so, cost both of yourselves money, but you can't stop him from divorcing. Divorce is legal. You can talk to him and see if he will try marriage counseling. The cause of action is much less important to a court then the fairness of the divorce terms or underlying merits of the claims of the parties as to money or children. While a court will allow a cause of action to be contested, irreconcilable differences only really requires the parties to disagree. Courts generally do not force people to remain married against their free will.
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Regretably, if he wants to pursue the divorce he can; even over your objection. You are entitled to contest the grounds for divorce, but it is a subjective standard. Honestly, focusing your time and money on obtaining the most favorable resolution would be more productive than challenging the divorce.
It may sound silly, but simply your belief that the differences can be reconciled and his opinion that they can not can be used as an example of how irreconcilable the difference are. You should consult with a local divorce attorney to see what options you may have to litigate further.