Trust Quotient

This note has been inspired by one of the blogs that I follow. It’s a conversation between two girls.
Girl 1 (crying): I am breaking-up.
Girl 2 (shocked): what??? You were like the perfect couple! You were so in love with him! What happened?
Girl 1 (still crying): I think he was cheating on me.
Girl 2: you think! You left him because of some crazy notion that he was cheating on you?!
Girl 1: no, I am positive he was cheating on me. There is this girl from his office, a colleague he says, and he is spending an awful lot of time with her.
Girl 2: so what? That no reason to leave someone. I thought you were above the jealous type.
Girl 1: apparently, they were working on a project. So they spent whole day in office together. When he was with me, he was either on phone with her or texting her.
Girl 2: it might be work related. You never know
Girl 1: you are right I didn’t know then. That project ended a month ago.
Girl 2: maybe they became friends over time. You have male colleague friends.
Girl 1: yes, and he knows all of them and they know him. You know how I know the girl’s name? Through his caller-id.
Girl 2: give him some benefit of doubt. You’ve been with him for more than 2 years now.
Girl1: I have asked about her lightly a lot many times and he just shrugged it off, saying there is no one. But then the talks turned into fights and we were always yelling at each other. At last he came clean. He has been out with this girl a few times. She doesn’t know about me. You remember our anniversary last month, how he was “late” for our dinner and didn’t get time to wish me until 10.30? He was out with her.
Girl 2: what does he say about you guys? The relationship, I mean?
Girl 1: he says he is sorry and will never repeat a thing like this. He says that he loves me. It was just a casual thing with that girl, nothing serious. He is going to tell her that he is committed to me.
Girl 2: then why are you still breaking-up? He is ready to make amends.
Girl 1: our relation is beyond repair now. I don’t trust him anymore. I don’t think I can ever trust him again. If he has done this once, then who can say that he won’t repeat it? He doesn’t know what he wants but whatever it is, it isn’t me.

How far can such actions of our “bitter” halves be justified? Was the girl right in leaving him or should she have stuck-out, given him another chance? Isn’t love about forgiving and forgetting? Or is it more about trust which broken once, is one times too many? What about the guy’s side of the story? What is cheating in the first place?