What I don't understand, whether the OP was right or wrong to accept this half-hearted invitation, is that there is all of this fallout/anger/"lies" about somebody going along to a party. It's not like this was an intimate dinner between two close friends, and then you barged in. It was a typical college get together. There seems to have been a whole bunch of other folks there. You guys went to some bars, got some burgers or whatever, and hung around. It's the kind of thing that happens 99% of the time when college students are free. The typical response to you showing up would just be, "Oh, you're so and so's friend? Cool, let's go get drinks." In what world, especially the world of college kids who are constantly meeting people, does having someone new come along lead to humiliating and insulting them? I can't count the number of times that I was out with my school friends and someone brought along a friend. Sometimes you like the friend, sometimes you don't. Sometimes you might feel a little annoyed because you thought that the hang-out would just be you and your closest buds, but sometimes you appreciate the new blood and have a better time than ever. Whatever the reaction or your personal feelings, no one would ever think to start cussing this friend out just because they showed up.
So, I really think that there's something else here. You may not realize it OP, and you may not be in a position to fully judge, but it's not as easy as you coming to a party where you weren't quite invited. You mentioned that there was some rumor that you were a sexist or had been looking at girls like a stick of meat or something like that. I haven't seen that part elaborated on, maybe I missed it. It seems like you made some social faux pas somewhere along the way, maybe accidentally, maybe something that was misconstrued. As someone else mentioned, maybe this PoG (lol) thought that you were angling to date your friend, and she was being overly protective. I'm not excusing any of these folks for making you feel terrible, but something here just isn't adding up.