Does a wife's communication with another man via the internet and phone, wherein she mentions her husband's good and bad qualities, constitute infidelity in Islamic law? And what is the ruling on a woman whom another person has corrupted against her husband?

The wife's act of conversing with a young man and communicating with him is a form of betrayal, as she is entrusted with her husband's honor. The young man's act of corrupting her against her husband is among the major sins. The husband has the right to refuse divorcing her until she forfeits her dower to him, or part of it.