<human>: So I just started college, and my friend Kate is a grade above me (so she's a sophomore now.) We were pretty good friends in high school, but 100% non-platonic. She had a boyfriend Matt in her grade that I was on good terms with and that I would occasionally hang out in a group with him.

So we are all going to college in the area (different colleges, but all close together), and in the beginning of July, Matt broke up with Kate, but both apparently took it pretty hard.

I joined frat this year, and since I'd been away all summer, I invited K and another couple of people in our friend group to a party we were throwing last week. At this party, most of us were pretty drunk, although I was quite a bit more drunk than Kate was, but either way, we ended up making out for 15 minutes. 

She asked me to keep it secret, and I did, but she ended up telling Matt, who then apparently got angry (at her and me, although I haven't heard anything from him). They were supposed to hang out two nights ago, but
he then decided that he didn't want to, so she and a group of her friends came back to my frat.

Her friends go to a different school than either of us do, so she told me that she didn't want to walk back to her school since it was further than mine, and basically ended up sleeping in my room. (We didn't go further than making out - here, we were both slightly tipsy). 

Anyways, I feel absolutely horrible now. Matt and Kate had been dating for like a year, and even though they weren't dating at the time, I'm the only other person Kate has ever kissed. 

Also for added clarification, I have no intention of dating Kate - this was purely a hookup. But I just feel super guilty and while I feel like I shouldn't, I do. Should I message Matt and apologize or whatever? Have I done anything wrong? What do I do?

Can you condense the text into a few key points?
<bot>: Hooked up with a acquaintance/friend's ex, and acquaintance/friend got upset and I feel guilty now. What do I do/did I do anything wrong?