Also, be glad she left the kids at home with you. It's too easy to spoil kids when on holiday. Most rules are suspended and they get gifts and everything they do is fun. You could get them back thinking that the boyfriend is better than dad.
Will you apply for custody? I think you'd be best for the children. She should see them, but cheating on a commitment like marriage isn't something you want the kids to believe deserves to be rewarded.