Heart broken

...I found out today my fiance now ex fiance was cheating on me with his high school sweetheart... I was So upset and still am I cried for five hours straight and ended up in the hospital with bleeding and a lot of pain plus I couldn't breathe. Thankfully everything is okay with my little sweet potato but I am so destroyed by this news.. I'm 18 weeks pregnant.. seriously how can someone cheat on a pregnant woman? :'(