Husband fathered a child out of marriage

It will amount to adultery only if the other woman was a married lady.   If the other woman is not a married lady, then there is no question of adultery.

There is not much that you can do. If the other woman was married to some other person, then it would be adultery by your husband. Even then the other woman's husband would be the aggrieved party and not you. As your husband has applied for divorce you can try to delay the process just to harass him.

Dear Sir/Madam,

Since your case is complicated case as such I require documents and same may be send to my email for detailed legal advise.

With regards,

Kishan Dutt Kalaskar