Fooling around with a girl who is in a relationship while drunk?

So I was fooling around with a girl at a bush party while I was quite drunk. I didn't know she was in a relationship until the morning, as she didn't mention a thing. We were around a campfire and it was quite public - she sat on my lap for a few hours. It progressed from innocent holding to touching her back and eventually to getting her off through her pants. Mind you, she was loving it and I saw no reason to stop, besides the fact that I was still quite drunk. She eventually got tired and went to bed when it was getting bright out and I went home a few hours later.

Well obviously someone noticed that we were fooling around and told her boyfriend the next day(who is a complete loser by the way).

I get a playful text that afternoon, which I responded to despite my instincts telling me to ignore it for now, followed by a text from her boyfriend a few hours later. He sent an innocent text asking how I was doing, clearly thinking that I wouldn't know who it was.

He again texted me today asking to "meet up" because he needed to "talk". Now, I'm not a small guy and can handle my own, but I just don't see why I need to get involved. Sure, I would likely win in a fair fight, but I doubt it would be fair and I don't see what I would be fighting for honestly. I would really rather no get injured for some stupid reason. I just don't think he will let it slide if I ignore it. Hell it wasn't even my fault, I had no clue she wasn't single and she didn't say a thing even though she was a hell of a lot more sober than I was.

Just looking for some advice on what to do.

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+1 y
Just to clarify, we are both seniors at the same school, so I can't really just avoid her. And honestly, I don't really hold anything against her. Not going to go around calling her a whore just to get out of the situation.
Fooling around with a girl who is in a relationship while drunk?
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