<human>: Give me a shortened version of the text

Throwaway because I'm ashamed. 

I dated a guy from October 2011 to April 2014, we just met up again in May 2015 and had make up-ish sex at his house while his roommates were out. 

As I was leaving, I saw a pair of shoes in his room obviously belonging to a female, and asked whose they were. He said they were a roommate's girlfriend's. Odd, but I brush it off. 

We aren't friends on any social media sites since we broke up, but I thought we might have a thing again so I look him up on Facebook and to my surprise, he's engaged to a girl I've never heard of. I check out her profile, which is all public, and she's posting about how exited she is that she's having his baby. I basically lost my mind at this point.

I don't condone cheating at any time, and if he's having a kid with someone he's engaged to and is messing around, I basically want to kick him where the sun don't shine. I'm conflicted now. I've tried putting myself in her shoes, and I think I'd want to know if my fiance was messing around while I was pregnant. However, I don't want them to break up and make the baby's life harder by having parents that aren't together or on good terms. I blocked his profile as I do not want any contact with him. Right now, I've got a draft typed up that I could FB message to the girl. Do you think I should send it, or should I go with "what she doesn't know won't hurt her"?
<bot>: Hooked up w/ ex, found out he's engaged w/ kid on the way, do I tell fiancee?