Confessions: I’m afraid my wife will find out that I’m still with my first love

I have two children and a good wife. I married her but it was because she got pregnant and I did not want to abandon her at her time of need. However, I had another lady who I really loved. This other relationship continued over the years and she now wants to move into town. She says she just wants to be near me and that the relationship is becoming too expensive to maintain as long distance. She is very understanding and says she would not interfere with our marriage. I love her but I am afraid that my wife will find out about this and she will cause a lot of trouble. Please advise me on how I can keep this relationship under cover. I don’t want to lose her.