Sir, I am in a relationship since 3 years. I was planning my life with her and I was going to propose her for marriage. But I recently found out that she is cheating on me. We live in different cities and my work is keeping me little busy these days, so I could not give her more time. But whatever I am doing is not only for me, it is for ‘our’ future. I don’t know if my business has created this or something else. But I can’t think of her with anyone else. And I am afraid to ask her and clear all this out. Because this may end our relationship as I don’t have sure shot proofs. I just have her, but some of my friends have told me that she’s regularly going out with a guy since many days.

First you need to confirm that your doubt is real, you may also have to go for a break up if she is really cheating on you, because the foundation of a relation is trust. And if trust is not maintained then it is difficult to live happily together
If you don’t get proper proofs and are still suspicious then you may go ahead and clear your doubts.  It is always better to talk and clear things, instead of keeping misunderstanding in the relation. If she is serious about you she will not leave you because you asked her something. Also if you feel insecure that you are losing her than you should even share this feeling with her and ask her what is causing the distance in the relationship?