In 1 Corinthians 7:10-15 gives teachings on separation in marriage and handling of a non believer partner.
1 Corinthians 7:10-17
[10]For married people I have a command which is not my own but the Lord’s: a wife must not leave her husband;
[11]but if she does, she must remain single or else be reconciled to her husband; and a husband must not divorce his wife.
[12]To the others I say (I, myself, not the Lord): if a Christian man has a wife who is an unbeliever and she agrees to go on living with him, he must not divorce her.
[13]And if a Christian woman is married to a man who is an unbeliever and he agrees to go on living with her, she must not divorce him.
[14]For the unbelieving husband is made acceptable to God by being united to his wife, and the unbelieving wife is made acceptable to God by being united to her Christian husband. If this were not so, their children would be like pagan children; but as it is, they are acceptable to God.
[15]However, if the one who is not a believer wishes to leave the Christian partner, let it be so. In such cases the Christian partner, whether husband or wife, is free to act. God has called you to live in peace.
[16]How can you be sure, Christian wife, that you will not save your husband? Or how can you be sure, Christian husband, that you will not save your wife?
[17]Each of you should go on living according to the Lord’s gift to you, and as you were when God called you. This is the rule I teach in all the churches.