I´m a bit lost

Apologize for my grammar, english is my second language.

I’ve been dating my gf for a little over a year now. A few months ago I caught her flirting with another dude online, I’m talking about flirting-soft sexting stuff. I told her I feel uncomfortable, she brushed it off and sweared up and down that it was nothing. I wasn´ t at my best state of mind at the moment so I actually thought I was in the wrong.
I started therapy a couple months ago, 2 sessions per month but it was enough to make me have more self respect in myself. I started thinking about that period of time and I got mad. Both at her and at myself. At her for brushing it off like it was nothing, and at myself for not ending things the second I discovered what she was doing. She stopped talking with the dude around 5 months ago, and since then she didn´t really did anything to make me question her. We get along well, sometimes we fight over stupid things but overall is good. We visit each other every week (we live 80km apart). Thing is, since I started thinking about that period of time, all love I felt towards her changed into heatred. When I dont think about it everything´s fine, we chill in bed together, watch movies, go on dates, etc. I dont know if it would be right to end it now, when everything is going well. Back then I didnt had the right state of mind to end it, but now I feel more ready than ever. Is it wrong to end things over something that happened a long time ago, even if everything is working out good now? I dont know if I should keep this going. I still love her and things are well when I dont think about it. Idk, I need a second opinion lol.

​

tl;dr: Is it wrong to break up over something that happened a long time ago?