Cheating?

I just found out that my fiance had been talking to another girl earlier today about her baby (that may be his), and how he wanted to be in its life. (I didn't know about this girl, if it was just talk about the baby it'd be okay). Later on in the conversation, they started talking about meeting up and having sex, and how they "didn't have to worry where cums now" and how she wanted him to fuck her, and so on and so forth.

he's trying to justify it by saying "well, I didn't actually do it" and I can't do anything but cry. I wanted forever with him and now I can't even look at him without being nauseous..