WELL POLY CHIK, everybody is judging you but i dont have any right to, we all are human and whatever happens in life, has already been calculated.
i will only suggest to you, though am a single guy and never had a girl that cheated on me before, so here is my own contribution.
1. Any woman that cheats on her husband, has already laid a foundation for the destruction of that marriage or affair, it doesnt matter who did the lintel or roofing.
2. Just tell us what lead to the topic of presenting the wife infidelity to the husband. Cos i know is normally amorous discussion that can bring that up such, sometimes.
3. Did you complained to the man, cos you think you can love him better and never cheat on him, or you did the complain as a self PROMO, or slip of tongue.
4. IS the man loving you with all his senses or under steady brainwashing or seduction or alcohol.
       
             well to help you answer some of the questions,
1. the woman being your best gave you the opportunity by sleeping around, cos if she cherish the man, she would has padlock her psy,
2. if the man is the one that ask you and you said the truth, you are right. but if not, that means you have eye on this guy more than the baby mama.
3 Do you think you can love him better and would raise a generation with her as a true christain woman, then ride on girl. But if you still have an eye on another zip out there, after taking this man, you will end up living worst than your friend. even miserable.
4. The man seems to be a player, for acting fast to what you said, no investigation, chase the mother of kid away like that, making love to you so fast. common, he has eye on your booty and maybe you noticed that and use it on him.

             my advice is DONt rush into married with this guy, watch his feelings towards his baby mama, cos the man might be enjoying you, and when his through, the only thing he will tell the ex wife, am sorry forgive me, and she will take him back. Then you will lose.
the man is irresponsible to me, and might make you second baby mama, and move to the next girl. IN such case, give this man 18 or 20months atleast to know his intention,  3 months sounds bitchy.
                 NOw beware of you best friend, cos she is not happy with you, and can do something nasty. dont rush. and for the cheating ladies, YOU ALL DESERVES FRIEND LIKE THIS. FOR PEOPLE SAYING YOU SHOULD TALK TO YOUR FRIEND, IS SHE A KID. ALWAYS TELL THE TRUTH AND IT SHALL SET YOU FREE.