Infidelity is a touchy subject and there are those who can forgive and those who cannot. However, what it all really comes down to is the loss of trust not the actual 'act'. If someone can look you in the eye and lie and lie....then I do believe they have stepped over a line that cannot be redrawn. Trust is the bedrock of any relationship and without it nothing else can survive.
Your friend has been brave, and she's probably right to stay put if she can cope - he is obviously not to be trusted and could cause great inconvenience by being obstructive in her home. Its great she has your friendship - she's going to need a fair bit of support now. All the best.
Adverts that are being shown on the tele



as seems appropriate. Good luck!