Seduced by boss's wife when I dropped off keys to his house

I popped over to my boss’s house to drop off some keys and ended up having the wildest sex ever with his wife. Now I fear for my job and my future.
I am 18 and an apprentice motor mechanic. I have always got on well with my boss. I got the job over a huge number of applicants because he thought we could work well together and he’d had problems with apprentices in the past. He said he knew I would be decent and hard-working and that he could trust me.

He had to go and sort out a problem one evening so I agreed to lock up and drop the keys off at his house.
When I got there his wife told me he had rung to say he’d be very late. She invited me in for a drink saying she’d like the company. She must be around 40.
We chatted and she told me she was lonely and her sex life was slacking. She was upset and started crying so I tried to comfort her by telling her it was going to be OK but she began to cry harder and asked for a cuddle.
I could hardly refuse but I made it a friendly hug. This wasn’t what she had in mind, though, and she started kissing me and said how horny she was for me and that she had fancied me for a while.
One thing led to another and we ended up having incredible sex. I have never experienced anything like it. Perhaps it is always better with a mature woman. Now I cannot stop thinking about it.
I have not spoken to her since but I’m afraid she will tell my boss and I will lose everything I have been working for. I don’t know what to do.