<human>: Can you succinctly summarize the text in 1-3 sentences?

There is a male acquaintance of mine who has been hating me for some time. He used to be able to be around me for some time, and I have no problems with him today, but apparently he has, every time I'm around him he tells me to go away and when I speak to others he just stares at me with an ugly face. 

We are both part of the same big sports club, we had done some practice together but not much more. Last fall our club had an end-of season "recap meeting" (party) with an overnight stay at a hotel/resort. It was a fun night, to say the least, and at 3am I found myself alone in a room with a female acquaintance who started touching me, and it didn't take long before we ended up in bed together. Throughout our sexual activity she kept talking about this other guy, that she had been looking for him, he had said he was coming to her room, that he didn't answer his phone or her messages, etc. We finished and I walked back to my room to get some sleep. The day after she texted me, asked if something inappropriate happened, that I shouldn't tell anyone, etc. She apparently promised to keep quiet as well. 

Then, when I met this guy again some weeks later, his demeanor had changed considerably, he was extremely unfriendly and hostile towards me, and this has continued up to today. 

I can only assume that this girl has told him what happened or that he has found out in another way, and that he had some sort of expectation or deal of having sex with her that night that wasn't fulfilled. That is only my assumption, but I can't think of any other reason behind his behavior towards me. 

How should I approach this situation? Should I ask the girl whether she has told him, or if she knows that he has found out what I did with her? Should I confront him with whether the reason for his hate is the relation I had with this girl?

The whole origin of the incident is incredibly embarassing for me, I just want to forget it, but presumably there is at least one other person who hasn't forgotten it.
<bot>: A male acquaintance has started hating me, coincidentally just after me having sex with a girl he had been texting. How should I approach this, considering the incident was very embarassing?