1, the most damming part is the fact that (if your right) she told 3 people 3 things. Especially that she went from 'not sure if I consented' to 'I said no multiple times' - inbetween talking to a friend and a boyfriend.
2, who cares. If my wife got into the bed of another man after a night out without me, she would be kicked out of my house as quickly as possible. People in committed relationships can't do that sort of ****. Especially after drinking.. it leads to situations like these. Did she cosnent to sex? who knows.. but she certainly cosnented to go home with a guy, and get into his bed. The only exceptions I can see to this is like a childhood friend thats more like a brother, or a gay friend...
3, committed relationships take work, and need rules. Trust is earned not assumed, and she has shown clearly that she does not deserve trust.
I know these are not popular opinions but generally speaking if you love your partner, and you want your relationship to last 40-50 years.. follow these rules:
1, no heavy drinking when you are not together. The odd glass of wine or pint is ok, but if your going propperly drinking or clubbing, make sure you two are together
2, no going out on girly/lads nights out with a group thats majority single. Fine if your all in relationships, but if your the one in relationships with 4-5 single girls/lads, its a very bad idea
3, no lads/girls holidays unless you both are going.. or its something that doesn't involve heavy drinking/clubbing
4, the guy is the main link to the majority of your guy friends, and the girl is the main link to the majority of your girlfriends
5, your social circles should become one, as soon as possible, and you should have joint friends where possible, not individual friends
6, No staying over or extended time with single guys for the girl, and the same with single girls for the guy.
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follow those rules, and enjoy a happy long-lasting relationship where you can both show your dicipline and commitment and in return earn each others full trust.