Is it ok to be with your friend's man?

Tweet

well I just know her for about three weeks. I knew her man before her, we made out couple times before she knew him. however when she met him, i didnt tell her we were dating, because i wasnt sure about him, and i could tell she liked him alot. so i decided not to tell her. she could have him, even tho i liked him. because at that time I wasnt rally into anyone. but now i see him everyday. He gets jealous when he see's me with other men. he's angry at me for not telling my friend the truth. she's a nice person. none of us want to hurt her. but he is doing so without knowing because of his life style, and she wont say anything to him because she's afraid of the truth. He's a player, he thinks she knows and will be ok with it. she cant tame him, but i can! what should i do, let him continue hurt her? or should my friend and i leave him alone? or should i take him? I really like him tho, i want him because he's a challenge. I think i can tame him.