I need ur opinion about this situation.....?

Ok.. my best friend "Beth" is 29.She has been married twice and is going through her 2nd divorce.Her first marriage was to a man named "Anthony".They got married when she was on 17.In the 2nd year of their marriage he started being really abusive to her. She almost died on many occasions.They had 3kids together.He is in jail for selling drugs in a school zone.Well last year she met "Charles". At first she thought he was kind and sweet. Well she was pregnant after 2months of knowing him.She miscarried 4months in. She kicked him out 1 1/2 months ago because he stole $10,000 worth of jewelery off his uncles wife. She had a BF before Charles named Ted. We went to school Ted. He is 2years older than us. She has a new BF named Justin. She told Justin she was gunna stay at her moms house(on last sunday). She lied and invited Ted over. She told me they had sex that nite. Ted left a Hicky on her neck. She hid it from Justin for 4days then it went away.Justin has no idea about her having sex with Ted.Should he know? Should I tell him? I wanna be a good friend.