Help! I have accidentally broken my son's girlfriend's nose!?

I recently split up with my wife who I have been married to for nine years. My son thought that it would be a good idea to have a house party to try and cheer me up a bit and to possibly help me find a new partner. I wasn't to happy with idea but in the end I decided to go along with it to make my son happy. My son invited a few of my friends, some work colleagues and his girlfriend. During the evening time, one of my work colleagues called Jenny started to flirt with me. I have always liked her and I thought that I should give things a go with her. So anyway I took her into my bedroom and we started to strip off for sex and she then picked up my tie and made it into a blindfold and put it on me. Because she had lots to drink that night she rushed out of the bedroom and went to the bathroom to throw up. But I didn't know that she was going to the bathroom and instead I thought she was waiting in the hallway for me to come and get her, in a way like a cheeky game of hide and seek if you know what I mean? And also by this time I thought that everyone in the house had gone home. After about 30 seconds of waiting I left the bedroom with a smile on my face ready to find Jenny in the hallway. But what I didn't know was that my son and his girlfriend were still here cleaning up my house. I went towards the stairs with my hands out in front of me ( I was still blindfolded). I then heard the clanking sound of bottles touching and thought that it was Jenny leading me towards her. I reached out toward who I thought was Jenny and grabbed a boob. Then an almighty scream was let off and then without thinking I punched as hard as I could at where the scream was coming from ( for some reason I though I was defending off a burglar). I took off my blindfold and It turned out that I had knocked out my son's girlfriend. And it also turns out that Jenny had passed out in the bathroom. My son instantly came running up the stairs to see what had happened and as soon as I heard them footsteps I went straight to my bedroom and pretended to be asleep. My son's girlfriend woke up five minutes later and then my son came to "wake" me up. She had no clue as to what happened and she thought that she had tripped over something. We all got into the car and and my son (who never drinks alcohol) drove us to the hospital and Jenny was also in the car because my son thought she needed medical attention as well. They're both alright now, but I just can't seem to shake off the guilt of what happened to my sons girlfriend. The only good thing to come out of this is that I am dating Jenny. What should I do? Not tell my son but hope that his girlfriend doesn't know what I did? Or just confess? please help me.