Almost Married but Cheating...

A friend of mine is getting married soon as she already did her introduction early this year. When she was at school outside the country, she made cheating her hobby while  making him stay celibate.

Now back in Nigeria, she still cheats with one of her colleagues (works in a company that starts with P) while she is the one requesting for quick marriage. She now intends to get pregnant as soon as possible to "nail him down".

All it would take is one anonymous message although the guy seems to be a fool for her.. 

Not sure whether telling is moral or staying silent is immoral.