So recently I broke up with an ex. We had trust issues getting out of hand, but there was one specific incident that triggered it. I'm curious as to if I did something wrong, and if so, where I crossed the line:

So, I studied abroad for a semester (alone). Came back, caught up with a good friend and realized he was seeing a girl in one of my classes. Thinking, at the time at least, that she could be joining our friend circle, I texted her and asked some questions try to get to know her better

Well, my ex saw the texts and flipped out, accusing me of flirting. I freaked out, promising her it was no such thing and begged her to let it go

It was not a healthy relationship (as evidenced by her checking my phone), and I ended it a few months later. Even then, her mom told my mom of my "flirting"

Was texting my friend's girl (and asking some personal questions) a no-no? I'm trying to understand if I did cross a line of socially acceptable behavior, or if the ex was just crazy