How do I get out of this mess without hurting her?

I met a lady through an online adult cams website. Yes, I know, sleazy, but please don't make judgements straight away. Obviously when I went online with her I had no intention of our relationship becoming anything more than transitory. I guess because I am not too enamoured with my own image I told her I was a younger guy of 20 (im 43). She is 38. We clicked immediately. Anyway, things have very quickly progressed and we now exchange emails, chat on Messenger, and via the original website. She is very obviously very fond of the guy she thinks she is chatting to, and I have allowed the deceit to continue. When she asked for a pic I went online and found a good looking guy and sent that. I am not looking to protect my own feelings here, I know I am an idiot at best, and I am in a terrible mess trying to work out whether I continue to deceive her, or tell her the grisly truth and hurt her. I have invented a whole world around this guy, he even has a MySpace page. She is utterly smitten, as, to be honest, am I. I feel completely in love and so tender toward her, and I just know it is going to end horribly. And yes, I am married, and she is a single mum looking for some affection and love. All I have told her about my feelings, the poems I have written, are true to my heart. She has started talking about meeting, and told her friends about me. I don't want to hurt her, she is a very lovely lady. What the hell do I do? Tell her, continue to deceive her, or pretend to lose interest in the hope we will drift apart?