Gf spent the weekend with her guy friend. My life is officially over… [MMF]

Me and my GF are both 30. We have good jobs and make a reasonable amount of money. We have been together for 5 years.
I love her very much. She is to be frank the most beautiful woman I have ever seen. She could easily be a model. She is many guys ideal woman and a certain 10/10. Whenever she goes out she gets hit on CONSTANTLY. Whether i’m there or not actually.
Me, not so much although I have no problem attracting women. I am above average (7/10) and take care of myself, but I couldn’t be a male model or anything.
Generally our relationship has been fantastic. Neither of us has been unfaithful and we are very much in love. I certainly love her very very much.
The last six or so months have been stressful however. Work has been into overdrive for both of us, and although we’ve made a reasonable amount of money towards buying our first house either of us getting home before 10pm has been very rare. Basically we’ve been exhausted and have neglected both sex and our relationship, although not for any other reason than time and being exhausted. My feelings haven’t altered one iota and neither have hers.
Fast forward to around 2.5 months ago when we were both invited to separate reunions with old friends across the country (neither of us are originally from the area we’re living in now). It was a great opportunity for both of us to blow off steam after working so hard and neglecting life for a few months, although we were both disappointed it wasn’t going to be with each other.
So we kissed, told each other how much we loved and will miss each other, and I went across the country to my hotel and she went to hers.
Lets just say, we had VERY different weekends.
Hers involved going to a party where in her words, the most good looking guy she has ever seen approached her. Apparently he was a friend of a friend of someone else at the party. She basically said every woman was getting wet just looking at him and she was just on a high that this guy approached her. She didn’t plan on anything, but everyone was drinking heavily and she ended up in bed with him……. FOR MOST OF THE WEEKEND.
When she came back she was the most loving attentive girlfriend you have ever seen. I was still too tired/exhausted for sex, but literally she was like a stepford wife in the weeks that followed. I stupidly just put it down to her missing me and loved that she loved me so much.
Fast forward again, she broke down and said she couldn’t cope with the lie anymore and told me everything. Prompted I’m sure by her finding out that morning that she’s pregnant. There is ZERO possibility of it being mine.
She is the most sorry and frightened woman you have ever seen. She even asked me to physically assault her because she is so angry and upset that she cheated on me. She will do ANYTHING I want to make things ok. It’s a bit scary actually. She is frightened and literally shaking at the prospect of me leaving her.
If i’m honest with myself I think most of the fear is about the baby. She is crying saying she can’t get rid of it and she is terrified of keeping it and raising it alone.
I was completely and utterly numb and heartbroken.
I said to her that before I go any further, I need the truth. Literally every second of what happened that weekend or I’m out the door. I knew this was a double edged sword and that the reality and cold facts could destroy me, but I’m one of these people who can’t not know.
The facts were horrifying and made me physically sick. I actually threw up. Basically my girlfriend was this guys personal porn star for the weekend. Some highlights:-