My best friend is not the same person he was

To start my friend got this girlfriend about a year and a bit ago, they were so in love that he completely ditched us and stopped talking to us over a girl. They did everything for each other and seemed extremely happy. A couple of nights ago I threw a party ( my best friend came his gf didn’t) , and invited some people over including my best friend (19m) and my other friend (19f) who I’ve known for a couple of months, at this party we got all pretty drunk. My best friend and this girl had never crossed paths before, they just knew of each other. Anyways at this party they were both sitting next to each other on the couch, which now I’m sober I think is strange. Then I went to the bathroom and came back and they were gone. Me and my friends and gf all went looking for them. We looked around for a little bit outside and could not find them, suddenly I get a call from my friend saying he had been rped and that he was in his car .I obviously ran to his car making sure he was ok, next things next we were talking while he was crying. We went to sleep. Next day he tells his gf that he got rped, she doesn’t believe him. And I at first thought wow that’s awful. But then me and my gf started to think and recounted the steps of what he told us and what we saw. This girl was extremely drunk and could honestly barely walk she was so hammered, he was clearly not as drunk. He claimed that she got on him and he couldn’t move he was so drunk. Then I started thinking wait how did he make it to his car which was a 5 minute walk if he was so drunk he couldn’t move. Also he took HER to his car, she didn’t know where that was so she couldn’t have taken him there, he took her there. And what other intent would he have besides sex. He took a drunk horny girl to the backseat of his car and had sex with her. I feel awful for not believing him but no one else does either. His story just does not make sense, at all. It is clear that he is lying and everyone knows it. And to like about getting rped is absolutely awful, especially because my gf has been in a situation like that before. He lied to my gfs face about getting rped and I am livid about that. I don’t know what to do because I honestly don’t want to talk to him anymore, I can’t look at him the same way I did. I don’t know whether to call him out on his shit or just stay silent. I just do not understand what he was thinking. Him and his gf were so happy and he threw it all away for some random girl. And then is lying to his gf that he got raped. What do you think I should do in this situation? Sorry for the long story and if it was all over the place