If the marriage has broken down due to the husband having extra marital affairs, and every possible avenue to address the marital problems have failed and both spouses have reached a point where they are unable to fulfil their Shar’ee rights to his/her marriage partner, then the husband should release his wife by issuing her divorce.
He should not keep her in his marriage. Allah Ta’ala says, ?Imsaak bi ma?roof? (keep with principle ? fulfil marital obligations), or release (divorce) with principle. If the husband is spiteful and withholds the divorce, the wife may request Khula by offering to return her dowry to him. If he agrees, then only the Khula will be valid. If he does not agree, then she may apply for an annulment of marriage from her local Ulama body who will consider her case based on the rules of Faskh (annulment) of Nikah.
and Allah Ta’ala Knows Best
Mufti Ebrahim Desai