choices can be hard... but its not about being a bad person or a good person, its about doing the right thing... which i know can also be tricky.
But put it this way. If you tell him, it might hurt you both at the time, but hopefully you can move on from that hurt and conflict, and use the intimacy you have gained with each other, and while you will have lost some trust in some places, you will also have some trust you have proven by telling the truth, and you will be able to go on with a clear conscience in the sense you are not lying to him any more?
But if you lie, then you will just end up being dragged down by guilt, and feel more $#%^ about yourself than you already do, which will have an impact on both you and your relationship, and keep a barrier of dishonesty between you.
if you eventualy find you can't do anything else except come clean, maybe years down the line, your own feelings might have made the level of intimacy you have suffer, and telling him you have lied to him then, is going to be ten times worse.
I think that's what they mean when they say lies destroy relationships from the inside out, make them go rotten, or something like that.