Dear LIB readers: Should I tell her?

From a female LIB reader...

My very close friend has been married for 4 years and I just found out that her husband has a mistress. My friend is 7 months pregnant and is in a very happy phase in her life. It hurts me not to tell her but at the same time I don't want to be the one to burst her bubble especially with her condition. Though this won't be the first time he's cheating on her. He once got a girl pregnant when they were dating just cos my friend was a virgin back then and refused to sleep with him. Though he made the girl abort the baby and moved mountains to make my friend forgive and come back to him. They dated for 7 years, he disvirgined her and she has invested so much time, sweat, energy in the relationship that now that it has finally materialised into marriage I just don't want to be the one to uproot her world.