Girlfriend was accused of cheating, Not sure who to believe

So I've been with this girl for about 10 months, and we have been in a long distance relationship. We are both in college and go to schools 4 hours apart. We are both 19 too. So last weekend I went home to visit my family for the easter weekend, and she went home as well. On one of those nights that we both were home, I decided to stay home and spend time with my family. She went out with one her good friends (Amanda) to a bar, and ended up meeting up with one of my good friends (Nick) from high school and his two friends (Chris and Connor, who go to college with him. So once they all meet up and are at the bar for a few hours, my friend from high school, Nick, invites my girlfriend and Amanda back to his house to hangout. This wasnt a weird thing for him to do because he was good friends with my girlfriend in highschool because we all hungout together. So they all go back to Nick's house and just hungout in his basement and drank some more. This is the part of the story where everything seemed to get weird. (Also I wasnt there so this is what ive taken from everyones perspectives). So my girlfriend and amanda ended up staying at Nicks house till 6 am. At one point in the night my girlfriend went upstairs in the kitchen because she wanted some water. Chris, Nick's friend from school was up there too. My girlfriend and Chris apparently stayed up in the kitchen for a good half hour just talking. My friend nick went up there to see what was happening between them, and he said that they were talking, but it looked a little weird. (You know when two people are talking and it looks like they are going to hook up? that was apparently what it looked like from my friend's perspective. My girlfriend said it wasnt like that, and that they were just talking about their lives n stuff. After a while though everyone went back downstairs to the basement. After a while it was getting late, My friend nick wanted to go to bed and my girlfriend and amanda were going to leave soon. This is where everything apparently happened. So nick goes into his room and amanda follows him, and they were in there talking for about 10 minutes. This left my girlfriend and Chris alone for that amount of time. (also Nicks other friend connor was passed out at this point). So Chris and my girlfriend were alone, and Chris told my friend nick that my girlfriend kissed him because they were about to leave. My friend nick then relayed this information to me. after hearing this, I accused my girlfriend of cheating on me. Her response was honestly really good and believable. She got a little mad, but It didnt seem like she was lying about it at all. I wanted her to prove it by texting him, and he gave her responses like "do you want me to say it didnt happen." Like it looked pretty obvious. I went ahead and texted Chris, and He confirmed that it did happen and he was sorry, he didnt know she was my girlfriend. (also chris is from denver which is about 8 hours from where I live so it seems that he would have no reason to lie about something like this. My girlfriend still denied it and still denies to this day. She even brought some of her family into it, and she still says "that she would die knowing that shes told me the truth. She has honestly been a great girlfriend, and I never wouldve even thought that she would do something like this, which is why i almost want to believe her. Everyone ive talked to about tells me that she's crazy and i need to end it, but I'm just not really sure what to do. Please help