Messaging the other girl

Ladies I messed up. I dont know what else to say but I did. My fiance told me yesterday that he asked the neighbor if she wanted to hook up. I was so upset that I texted her some not so nice things. My fiance said she declined and nothing happened but still. He also told me that he had been texting his ex because he was going through a midlife crisis and thought I was too fat.i was able to forgive him for the texting but I am not sure about him asking the neighbor to hook up. I'm really at a loss. I know the logical thing to do is leave. But has anyone wanted to stay?

Edit: I did message her back and apologize. But she hasn't replied.