I really doubt she is "waiting" for you to "admit" anything. And honestly, if my husband of 15 years came up to me suddenly and said "Honey I'm attracted to younger women." I would probably feel very rejected and feel like he was calling me old and therefore no longer attracted to me. So no, I think you're about to open up a can of worms if you blow this out of proportion. She was with you that night and obviously it doesn't sound like you had any room to actually cheat no matter how drunk you were - so I doubt anything happened, and the fact that she isn't upset just goes to show you that she literally isn't upset about anything.
Women can't usually hide being upset about something just for the sheer passive agressiveness of it. She's not "waiting" for a confession.
Your guilt is just coming from you, no one else. It's best to just forget about this and don't act on any impulses to cheat if you are so happy in your marriage.