If you were happy before you found out, and have companionship and friendship, and you say he is good to you, is there any chance you can come to terms with it? Is he not telling you because he does not want to hurt you, but is one of those men who needs a physical outlet? If so and there is still affection between you, and you enjoy being together, can you settle for that, leave things as they are, treat yourself to a few things you want without feeling guilty and go out on your own with friends sometimes (if you don't already). But if, very understandably, you can't help feeling resentful and hurt, and this knowledge has destroyed the feelings you had for him, then just have it out with him and be prepared to live without him. Only you know how you feel, but don't act in haste, give it a few months and you may feel differently. Once you tell him it may be out of your hands. Perhaps the secrecy adds a bit of spice or perhaps it is a constant worry for him that you will find out and he will lose you. The other woman might just want sex without having a man around full time, or she might secretly hope you will find out and leave him, and then she can have him full time. Once it is out in the open, nothing will ever be the same again. Many women have lived with the knowledge of their husband's infidelity, and been quite happy, but you don't have too. It is a trade off for what he gives you, only you know what you want out of the rest of your life.