ok.. is this a prayer forum or am i allowed to give advise??
1st of all, there are reasons why Paul said not to be unequally yoked w/ unbelievers.. and it was to our benefit. I think this is one of the reasons.. they are not following God, so they dont have the voice of the holy spirit as their guide.. they dont have much of a concience, and will be more self seeking than God-seeking. I am amaized though how she could forget her own kids and you, to run away with this creep. I would talk to this guy whom she is ‘going with’ and explain to him your feelings in a man-to-man way.. show him how much your hurt by it, and make him feel the shame of what he did.. with God’s help.. perhaps he will see what a good guy you are, and leave her alone.
(the worst thing you can do is violent behavior toward him, including threaten him)
I would call a lawyer and ask him what your options are.
remember, your in not so bad a place.. because you have scripture to cover your case.. in case you ended up w/ divorce.
1cor 7:12:If any brother hath a wife that believeth not, and she be pleased to dwell with him, let him not put her away.
 And the woman which hath an husband that believeth not, and if he be pleased to dwell with her, let her not leave him.
 For the unbelieving husband is sanctified by the wife, and the unbelieving wife is sanctified by the husband: else were your children unclean; but now are they holy.
 But if the unbelieving depart, let him depart. A brother or a sister is not under bondage in such cases: but God hath called us to peace.
 For what knowest thou, O wife, whether thou shalt save thy husband? or how knowest thou, O man, whether thou shalt save thy wife?