The Ex-boyfriend issue

So this girl I was friends with dated this guy they were together for three months and throughout that three months they fought a lot. She was cheating on him and he was cheating on her. Fast forward a year later I text him for some details about a party I want to go to won't my other friend (let's call her friend B). Well one thing led to another and earlier this year January I want to say I ended up losing my virginity to him. Now that's not the only thing I knew the consequences of my actions and in fact I was aware that it might end badly but honestly I don't know why it mattered to her. She dated every one of my exes and I didn't care slept with them flirted with them but this one guy and she flips her shit.