Am i gonna have to kill my bf

Had my appt where they take all the blood n do a routine swap to make sure no stds utis n blah.   Just got a call i have trichomonisias or however you spell it.  This is apparently the most common std to get & is thankfully really easy to cure & they will give me the meds once i hit my second trimester in a week n a half .. 
We suffered a loss in january & following that i got screened was told everything was good & they let me know how long to not have sex n such.  I havent been with anyone other than my bf for 3 years now .  Im trying to understand how, if were both committed to this relationship, there'd be an std in the mix.  So he just might be getting hurt & left.  I dont bother with looking through his phone n all that extra shit because guys always find ways around that.  & i assumed, were having a baby together "he wouldnt dare cheat"  i need prayers because i may hurt him because i forgave him once & told him i wouldnt do that shit again.  Had to vent before i go crazy on him.