Originally posted by: aryapdane
Bajaj isn't a saint. He is a human, made of good and bad. In the beginning of his track, he was an incredibly selfish man who couldn't see anything beyond his wants and desires. So when he loved Prerna, he loved her selfishly. Then, he wanted Prerna in his life and he was ready to do anything to get her back. So he took those photographs and had someone blackmail her. The matter of the photographs came up thrice in the show. The first and second time when Prerna confronted him, he lied to her and convinced her he had nothing to do with the photographs. The third time he himself payed Komolika to go and tell Prerna the truth of the photographs but Prerna didn't believe her. At this point Bajaj's character had grown from a selfish man to someone who could love her selflessly. He thought she was still in love with Anurag and wanted her to marry the man she loved. She didn't confront him.. Maybe he'd have told her the truth this time. But Prerna didn't want to know anymore. I like to imagine that at this point she didn't care because she was already in love with him and was determined to either win him back or live her life alone, without him. So the photographs wala plot point goes hand in hand with his character growth. 
Now the matter of Madhavi.. The one night stand happened when RB was totally sloshed. He was so drunk and distressed that he thought he was with Prerna. And Madhavi, who by the way was stone cold sober, didn't correct his beliefs or stop him and slept with him. If that's not taking sexual advantage of a man, I don't know what is. So can the one night stand of dubious consent be counted as cheating? Did RB even cheat on Prerna when they had clearly broken up? It was not even like they were on a break or something. He had legitimately broken his engagement to her. That is not to say that RB shouldn't have told Prerna about it. He should have. And IMO filed a case of sexual assault against Madhavi while he was at it. But he didn't. And twenty years later, this came to bite him in his rear end. Maybe you can watch that track... when Prerna finds out and her reactions to that news and why she still chooses to stay with him.
So to answer your question, whatever you heard was indeed true. But if you see it with context, his actions weren't despicable at all.