My sister husband cheating on her

So my sister got married to guy it's been 3 years now they have a baby after passing out 12th this guy suggest me for doing cs and i agreed with him he even gifted me phone that my parents abouslity didn't accepted we paid for it he even helped me found coching and hostel for my studies but now my sister findout he is having affairs with someone some relative told about him with proof to my sister he acts so perfect and kind in front of others even I believed it like he acts so good that he is most perfect and nicest guy in the world whenever I see this guy my blood boils he even have a 11 months daughter he didn't seem much attached to her i can't focus on my studies that guy suggested me this course and just hate him so much his father had huge lost in a company around 2 crore he is also trying to repay it I felt bad for him after knowing this shit about him he kinda desreve this but still he has guts to do these things I don't know what do now