Madam, please post this query. I have posted it multiple times but it is not getting published. I really need help urgently.

I am working in an MNC. I am 32 years old male and looking for a suitable match. I fell in love with a girl in my team who is 28 years old. She says that she also loves me. Our families have also talked about marriage. But, recently I got to know that she had some affair kind of thing with another boy in the company who is around 25 years old. She didn't reveal it herself. I got to know it from other sources after which she confirmed that she is in just talks with that guy. But, I found that she is talking till late nights and early mornings which is absoultely abnormal. Also, they have been involved in kissing and all. She said that she has committed a mistake and won't repeat in future. I am really confused that when we were finalizing the marriage then how come she gets involved with other guy. And, on asking she says that she herself don't know the reason. I am totally devasated and not sure what to do now? I know she had some physical relations in the past as well. But, after commitment, i feel she shouldn't do all such things. I am in deep love with her but now getting difficult to trust.

Please help me out what should I do now.