1. Suresh is being a friend a nosy on but a friend...he knows the truth of Pragya so called married life...he saw her in a hotel room in Mumbai instead of Simla where she was supposed to be...he saw her get arrested...he heard the truth about the state of her marriage...etc...and he some how also blames himself for her hasty marriage...
As for not blurting the truth to Abhi...he really tried once he found out the real cause of his anger...but Abhi instead of listening or giving him a chance to explain...passed judgement...and filled in making his own assumptions.
Suresh blurted out about his and Prags relationship...because he thought...that someone filled his ears about that...and once he realized Abhi was unaware about it changed his statement...
2. Abhi...feeling all possessive and jealous all of a sudden...and his chant of meri biwi...I was like "kise ki biwi???!!!!??"...He was being a first class hypocrite ...telling Prags I don't care who you sleep with...but then goes and beats up that person...
Here I do agree with Lk & Rani (Putturani)...