This's a very good subject. Section 497 of the Indian Penal Code doesn't define adultery. It shows the person guilty of adultery.
What's, then, adultery? One or both must have been married. If an unmarried male and an unmarried female commit intercourse it's not adultery. If force is involved it's rape. But, barbarically, force by female is not recognised by law. Force by female is, in practice, a trillion times as strong as the force that can be exerted by male. What's more, 99% of females use force whereas 1% of males use force.
But only male is punished. Female is never. Rape by men only is recognised by not only law but also dictionaries. What's the use if TGK Reddi only recognises rape by women? He's a voice in the wilderness.
In this case he is also married. So it's a ground for divorce.
Had he been an unmarried man, the pre marital s*x wouldn't have been adultery and is not a ground for divorce.
If there're kids because of s*x between unmarried mates, is it a ground for divorce? According to law, this shouldn't be ground for divorce. This's a problem of maintenance, in my poor opinion.